bny

Agreed: newsprint holds a lot of ink and with larger areas of fill, can be very troublesome with wrinkling.   Heavy ink load also can be apt to smear in transfer, perhaps too wet on the sponge side and still too dry on the work side.  I used this on one sort of Mesoamerican pattern that I printed in brown ink, knowing from a test piece that it would smear and look a lot like a pattern in chocolate that got warm.  I served some people a bake sale brownie on it.
For fun a couple of hours ago I pulled a test print on the smooth newsprint wrapping paper from a recently arrived jar of peppercorns.  It worked as well as the other two smooth newsprints that I tried, apart from a couple of creases.
Your offset 3D shadow effect is nice.  I tried double print with red and blue line and op-art patterns and had reasonably good results.  One person said that it was making them dizzy and looked like something for comic book 3D filter glasses.  Your note suggests that xuan might be better behaved than other papers on the more heavily filled op-art, so I will give it a try, including printing rough side.

Thanks for all the info! I've been doing a lot of underglaze transfers over the last couple of months, and I tried using the newsprint I use to wrap pots when I sell them, and I was not happy with the results. The underglaze is much more likely to flake off when it dries, and the wrinkling is a big issue. I'm doing large patterns, not line work, so there's a lot of underglaze on the paper and it wrinkles up a lot. I've settled on half-raw rice paper, printed on the raw side. It holds the underglaze well, releases very quickly, and doesn't wrinkle much at all. I've just been buying it off Amazon, about 29 cents per sheet.

I've been using adhesive vinyl cut on my Cricut to make the screens, with Speedball Screen Filler, and it has worked very well. This is a shot of the vinyl being removed from the screen once the filler has dried:

Additional notes on paper for transfer...
Other workers report using newsprint, typically on larger scale work.  I have found that newsprint can be usable and in some situations superior to thin papers.  Art store Strathmore newsprint pads are mostly "rough" surface for drawing, but they also sell a "smooth" surface in 18x24 inch size.
The smooth surface is capable of giving a good transfer without rustic effect.  I suspect that house-moving store packing newsprint could work here.  What I have been using most recently is a very inexpensive product packaged for the school market: 500 6x9 inch sheets for around US$5.00.
Smooth newsprint holds considerably more ink than thin papers like hanshi, and has a nicely closed surface.  Wet strength and peel performance are better than hanshi.  Detractors: permeability is not ideal (hanshi is immediately permeable), the paper tends to wrinkle in wet/dry cycling, and it does not conform well to curvatures.  Sometimes "considerably more" ink is too bold.
It transfers ok on flat surfaces to bisque and to fired underglaze background, but generally smears on unfired underglaze (hanshi can sometimes work here).  The wrinkling can be relieved somewhat by fine mist spray onto the unprinted side of the paper, before sponging down. Spray, wait a moment, spray more, test for softness, then sponge down while holding the paper down. 
At first, it will be more apt to adhere to the sponge than to the work: get it just damp enough with sponge pressure and not too much water, to be uniformly darker (dry areas will be lighter in color), burnish, then work more freely with sponge, burnish, and test-peel.
The heavier ink loading gives a more bold transferred image, but complete transfer can be tricky.  Fortunately, the paper is strong enough to lay part of the peeled section back down, re-sponge, re-burnish, then try peeling again.  It also is apt to smear if overly dampened.
For finer detail and more subtle color density, and for curvature, I still favor hanshi.  An additional US distributor for hanshi (besides Yasutomo) is Aitoh, and I was pleasantly surprised to see some in the local art store calligraphy section.
Photo: left and center are smooth newsprint, Amaco Velvet dark green, dried down and with addenda previously described, right is hanshi, Amaco Velvet purple.  Camera focus masks defects, especially in the left piece: silk screen pattern, ink formulation, and design edge behavior all interact.  Note unfilled edge areas and edge smearing of transfer, likely curable with better technique.  Hanshi piece has a few small transfer gaps, but looks ok.  Edge wrap of the design on the hanshi piece hints at curvature handling.

Additional notes on paper for transfer...
Other workers report using newsprint, typically on larger scale work.  I have found that newsprint can be usable and in some situations superior to thin papers.  Art store Strathmore newsprint pads are mostly "rough" surface for drawing, but they also sell a "smooth" surface in 18x24 inch size.
The smooth surface is capable of giving a good transfer without rustic effect.  I suspect that house-moving store packing newsprint could work here.  What I have been using most recently is a very inexpensive product packaged for the school market: 500 6x9 inch sheets for around US$5.00.
Smooth newsprint holds considerably more ink than thin papers like hanshi, and has a nicely closed surface.  Wet strength and peel performance are better than hanshi.  Detractors: permeability is not ideal (hanshi is immediately permeable), the paper tends to wrinkle in wet/dry cycling, and it does not conform well to curvatures.  Sometimes "considerably more" ink is too bold.
It transfers ok on flat surfaces to bisque and to fired underglaze background, but generally smears on unfired underglaze (hanshi can sometimes work here).  The wrinkling can be relieved somewhat by fine mist spray onto the unprinted side of the paper, before sponging down. Spray, wait a moment, spray more, test for softness, then sponge down while holding the paper down. 
At first, it will be more apt to adhere to the sponge than to the work: get it just damp enough with sponge pressure and not too much water, to be uniformly darker (dry areas will be lighter in color), burnish, then work more freely with sponge, burnish, and test-peel.
The heavier ink loading gives a more bold transferred image, but complete transfer can be tricky.  Fortunately, the paper is strong enough to lay part of the peeled section back down, re-sponge, re-burnish, then try peeling again.  It also is apt to smear if overly dampened.
For finer detail and more subtle color density, and for curvature, I still favor hanshi.  An additional US distributor for hanshi (besides Yasutomo) is Aitoh, and I was pleasantly surprised to see some in the local art store calligraphy section.
Photo: left and center are smooth newsprint, Amaco Velvet dark green, dried down and with addenda previously described, right is hanshi, Amaco Velvet purple.  Camera focus masks defects, especially in the left piece: silk screen pattern, ink formulation, and design edge behavior all interact.  Note unfilled edge areas and edge smearing of transfer, likely curable with better technique.  Hanshi piece has a few small transfer gaps, but looks ok.  Edge wrap of the design on the hanshi piece hints at curvature handling.

Looking for wet strength to aid in application to compound curves (like a teacup), I pulled out a roll of Talas TPB005002 wet strength tissue that I had bought some years ago.  This has long fibers and excellent wet strength, but its surface is too open to accept and hold fine detail.  Sizing the paper improves its behavior.
A couple of tries with homemade "British gum" sizing gave decent printing behavior, but the gum did what it does best, and turned into a tenacious adhesive that would rip the underglaze off the work, or if wetted sufficiently to sort-of peel, give a useless smear.
CMC sizing greatly improves the behavior of this paper.  It can give fine detail, though less reliably than on hanshi paper.  The peel behavior on underglazed low fire white clay, bisque fired at cone 06 (the body and underglaze are both thirsty, and the underglaze is more tenacious), can be quite good. 
Dish of hot water, sprinkle CMC on the surface, whisk, strain the globs out, you get clear "snot" as mentioned on the thread earlier.  I use a piece of 110 mesh screen-print fabric to support the paper for a brush application of CMC goop, then oven dry at 200 F / 93 C.
A single coat of sizing seems to work best: I tried 3 coats and ended up with a nearly glossy surface, decent print behavior, but poor transfer behavior.
Transfer behavior was less good on a commercial bisque espresso cup, underglazed and oven dried beforehand.  Wet behavior and conformation to curves was good, but peel behavior was poor.
I did half the cup by peeling and ended up with a not-great transfer (this piece does not even hold underglaze all that well).  The second half, I tried firing with the paper still on.  This almost worked, but there were areas where it looked like the design was disrupted by ash (and there was a little bit of ash left in the kiln).  The quality was promising, but not excellent.
9 gsm "Tissutex", my original source now apparently defunct, has a more closed surface, fair wet strength, good conformation, but short fibers, and tears easily in all directions.  When sized, it can work well, but it has a diabolical tendency to fold back and adhere to itself when wet, so it is difficult to coat with sizing.
Top pieces are transferred directly to cone 06 (fast schedule) fired once bisque, no underglaze, worked better than expected.  Larger pieces (70 mm diameter) are on underglaze (Amaco Velvet Lilac, Rose each lightened with White).  Larger pieces had been fired 3x previously at cone 06 fast (reused back sides of previous experiments).  Slight buff color background on the small pieces is from this low fire white clay.
Talas wet strength tissue paper, CMC sized one coat.  The wave grid has uneven density, likely uneven sizing on the paper.  On the balloons and hummingbirds you see a sort of rustic/weathered quality, mostly from the paper surface.  Small and large wave grid pieces were transferred from different clips off the same print: Amaco Velvet Rose underglaze color.  Balloons: Amaco Velvet Amethyst. 
Inks modified by dry-down, yellow dextrin, and gum arabic.  Mayco Crystal Clear overglaze on all.  Fired after decoration without overglaze, overglazed, fired again.

Take care with the total mass that you are adding, the support structure and condition of the balcony, and seismic risk.  Recall incidents where party guest loads have collapsed balconies. 
Ordinarily a kiln is not a comparable dynamic load, but a quake can change that in an instant. 
I read a journal paper some years ago where someone used bulldozer tread marks to show that one of the Ferndale quakes made a bulldozer hop on the ground, with what I recall as an estimated 2G acceleration.  I believe that I also recall reading that an estimate of acceleration in the '94 Northridge quake at a location in Encino on susceptible chalk ground, also developed around 2G.

I work on bisque fired pieces, originally as-fired, but now usually with a layer of underglaze briefly oven dried.  I sponge on the transfer, burnish with a small polished wooden knob tool, using a piece of old knit T-shirt fabric as a buffer against scrunching and gouging the paper, sponge again, burnish again through a more dry piece of T-shirt, pick an edge of the paper and roll back a little to see if it is transferring completely, sponge/burnish again if not, then peel.
That technique is what has worked best at my small scale and fine detail objective, with Yasutomo hanshi paper, half-ripe xuan paper, and brief experiments with medical exam table paper (smooth, not creped) and paper from old sewing patterns.

I work on bisque fired pieces, originally as-fired, but now usually with a layer of underglaze briefly oven dried.  I sponge on the transfer, burnish with a small polished wooden knob tool, using a piece of old knit T-shirt fabric as a buffer against scrunching and gouging the paper, sponge again, burnish again through a more dry piece of T-shirt, pick an edge of the paper and roll back a little to see if it is transferring completely, sponge/burnish again if not, then peel.
That technique is what has worked best at my small scale and fine detail objective, with Yasutomo hanshi paper, half-ripe xuan paper, and brief experiments with medical exam table paper (smooth, not creped) and paper from old sewing patterns.

I spent a couple of hours yesterday morning running some screen printing tests. I'm using a 110 mesh screen, Speedball underglazes, and raw Xuan paper. My findings:
- Speedball underglazes come fairly thick in the bottle, so with no modification they actually print pretty well for 1-2 prints. However, by the third print the underglaze would stop going through the screen and it would just print water. The thicker the underglaze the worse it got. If I washed off and dried the screen, then it would print again. I think the underglaze must be sealing up the screen.
- I don't have any guar gum or dextrin in the studio, but I do have CMC gum and Veegum T, which together are fabulous for suspending glazes and making them brushable. Typically I would make a syrup out of them, but I didn't want to add too much water to the underglaze so I mixed it up like thick snot- 2 tablespoons of CMC and 1 tablespoon of VGT to 1 1/2 pints of hot water (normally would use 1 gallon of water). Let it soak (overnight if you have time), and mix it with a stick blender.
I added 1 teaspoon of the snot to a pint of underglaze and ran a dozen prints without any problems. I also thinned out the underglazes a bit and was much happier with the thickness on the paper. No need to let them stiffen up at all. In fact, Speedball underglazes are a bit too thick in the bottle. I'd seen people say it should thicken up to a toothpaste consistency, but I didn't find that to be necessary or desirable.
- I was concerned that the CMC gum would make it more difficult to transfer, since in a typical application the gum makes the underglaze hard and resists water (which is why I always recommend applying underglazes to leather hard and bisque firing before glazing if you're working with dipping glazes). With the transfers they worked much, much better with the added gum. Great release from the paper. I lay the transfer on the leather hard pot, dab it with a wet sponge, then lightly roll it with a little brayer.  I'm doing some bold patterns, not thin line work, so it's easy to control how complete the image transfers by how long I leave the transfer on the pot.
- The raw Xuan paper is very fragile when wet. You have to be very careful about rubbing it when it's sitting wet on the pot. I've got some half raw coming and I'll see if that holds up better.
EDIT: Forgot to add- I have tried making the transfers with newsprint before, but I don't like how much the paper wrinkles as it dries. The underglaze was also more likely to flake off when dry. I'll try it again with the new gum-added version later this week and see if it behaves any better. The good thing about the newsprint is that it's much more durable than the Xuan paper.

I have had improved results by transferring onto a layer of unfired underglaze, rather than directly onto the bisque fired piece. 
Others have noted success with only drying down of the pattern underglaze "ink", without additives.  I never had good results with that directly on bisque, but the smaller butterfly piece in the photos is Amaco Velvet Amethyst dried down some, and applied over a background of Amaco Velvet Lilac toned way down with their White.  Hasty rough layer of Mayco Crystal Clear overglaze.
The larger shell piece uses the same underglazes, but with yellow dextrin and gum arabic additives in the ink.  I am pleased with the definition and density.
Both were printed from polymer clay decorating screens from Amazon sellers.  Both used Yasutomo hanshi paper. 
I have found that warm water might help transfer onto an underglaze layer.  I dab the transfer on sort of radially outwards, dress the edges down, then press a not too damp sponge onto the whole surface for a few seconds.  Then burnish with a polished wooden knob tool through a piece of old cotton knit T-shirt.  Then apply a damp sponge again, let rest a moment, burnish again through a second piece of cloth, then peel the paper. 
Hanshi does not always peel cleanly but it gives the best definition so far.  I peel and rub gently.  If entirely clean, overglaze can go on, usually gives a softer result.
If not entirely clean, I fire at cone 06 then apply overglaze and fire again.  This often gives crisper definition than applying overglaze over the unfired pattern.
Hanshi is a bit fragile for applying to complex curvature, so I have been working with various other papers bought years ago for another project.  Wet strength tissues sold for book and art restoration, usually abaca fiber, are showing some promise.
I had one partially good result on a small demitasse cup, compound curvature, using a wet strength tissue sized before printing (paper surface is not smooth, essentially a more finely textured teabag, so inking is uneven).  I sized it with homemade "British gum", which is just the homemade yellow dextrin roasted darker, sponged on and partially dried on recycled polyethylene Amazon envelopes.  Peeled at the right time, handled carefully, then dried on an open screen, one can get a nearly glazed paper surface.

I have been experimenting, and having good results with underglaze finer-detail screen print impression and transfer with two additives: yellow dextrin (dry powder) alongside gum arabic (dry powder now rather than bottled solution).  Both ingredients are safe but are nutrient materials that could spoil if not dry.  Partial drying of the underglaze helps to reduce bleeding in the screen impression, and to get ink that stands on the paper.  The two gums help it to stand on the paper, bind to the ware, yet unbind more readily from the dampened paper.  My current guess is that gum arabic both helps standing and binding to the ware, and that dextrin both helps standing, and loosens more rapidly with dampening to facilitate transfer.
Yellow dextrin is an industrial paper and fabric sizing and adhesive.  It is available in smaller quantities from a few sources, mostly offered as a composition binder for fireworks.   The good news is that you can make your own yellow dextrin by roasting dry corn starch in the kitchen oven.  Old industrial recipes suggest around 320 F / 170 C, but I have had better results around 375 F / 190 C by uncalibrated oven dial.  I let it roast for a few hours, with interruptions, testing occasionally.
Final result should be a yellowish buff color comparable to corn flour.  Mine is a bit lighter than the commercial product, but might benefit from hotter or longer roasting.  You are breaking the starch down into something more soluble: like old-school envelope and stamp glue.  Test by placing some in a dish, add small increments of water, and mix with a fingertip.  After some work you should get a yellow (mine so far) to brown (commercial dextrin) slippery goo that will readily coat the dish, become tacky, then dry to a uniform film, like envelope flap glue.  Also it smells quite appetizing.  Do not allow yourself to imagine delicious underglazed donuts.
I don't have a quantified recipe yet.  Starting point was 7 units of gum arabic to 5 units of yellow dextrin, but I don't have a ratio to underglaze, or an initial dry-down factor.  All I can say now is gloss-surfaced toothpaste consistency, and that I usually add gum arabic beyond the initial amount, until it looks and feels "right", and proves in a print and transfer.
If anyone is aware of a small quantity source for the darker, more deeply pyrolyzed starch sizing/adhesive called "British gum" please let me know.  Easy to find in container loads from India, not so easy otherwise.
Experimenting with papers, in addition to half-ripe xuan previously noted, has brought good results with two papers thinner than the xuan. 
First is Yasutomo hanshi calligraphy practice paper, nearly tissue-thin, which looks like a machine glazed (MG) paper.  One side is nearly shiny, and the other is dull.  This gives good impression and transfer, and may be a better choice than xuan for curvatures.  The wet strength is sufficient to safely pull a screen print (I oven dry and the print goes very waffle-crinkly), but sponged application requires care.
Second, surprisingly, is dirt-cheap smooth (not creped) medical examining table paper (also has MG surfaces). I gave up on this immediately for hot oil intaglio transfer years ago, because it did not survive the soap sizing needed for that process.  It is just good enough, however, for this process, and I already had plenty.   More fragile than xuan or hanshi, but readily available and economical.  Results may vary.  I spoke to a converter/wholesaler some time back, and he cautioned that this paper varies more than some due to price-driven commodity sourcing.
Hanshi peels more cleanly than exam table paper; xuan peels more cleanly than hanshi.
In this round I have been using Speedball and Amaco Velvet underglazes, both with good results.  A cookie cutter, Amaco Radiant Red, and a commercial hearts screen, have given  quick cute not-identical  Valentine charms that have brought exclamations, smiles, and even tears from recipients.
 
 

>If anyone is aware of a small quantity source for the darker, more deeply pyrolyzed starch sizing/adhesive called "British gum" please let me know. 
May be of relevance.

Pyrotechnics data for your hobby: Dextrin
https://pyrodata.com/chemicals/Dextrin
Sources:
Dextrin is easily prepared from starch. Potato and cornstarch will both work fine. The starch is spread out on a sheet in a layer about 1 cm thick and placed in the oven. The oven is then heated to 220°C(400°F) for several hours. The dextrin will turn slightly yellowish brown. One way to check if all the starch has been converted is to dissolve a small sample in boiling hot water and add a drop of KI3 solution (Lugol's iodine solution). A blue colour indicates presence of starch, which means the conversion hasn't completed yet. KI3 solution is conveniently prepared by dissolving a crystal of elemental iodine in a potassium iodide solution.

The complete removal of starch could be important in your application, so I would try the starch-iodine test.
PS
Dextrin and Making Dextrin
http://www.wichitabuggywhip.com/fireworks/dextrin.html
 

I have been experimenting, and having good results with underglaze finer-detail screen print impression and transfer with two additives: yellow dextrin (dry powder) alongside gum arabic (dry powder now rather than bottled solution).  Both ingredients are safe but are nutrient materials that could spoil if not dry.  Partial drying of the underglaze helps to reduce bleeding in the screen impression, and to get ink that stands on the paper.  The two gums help it to stand on the paper, bind to the ware, yet unbind more readily from the dampened paper.  My current guess is that gum arabic both helps standing and binding to the ware, and that dextrin both helps standing, and loosens more rapidly with dampening to facilitate transfer.
Yellow dextrin is an industrial paper and fabric sizing and adhesive.  It is available in smaller quantities from a few sources, mostly offered as a composition binder for fireworks.   The good news is that you can make your own yellow dextrin by roasting dry corn starch in the kitchen oven.  Old industrial recipes suggest around 320 F / 170 C, but I have had better results around 375 F / 190 C by uncalibrated oven dial.  I let it roast for a few hours, with interruptions, testing occasionally.
Final result should be a yellowish buff color comparable to corn flour.  Mine is a bit lighter than the commercial product, but might benefit from hotter or longer roasting.  You are breaking the starch down into something more soluble: like old-school envelope and stamp glue.  Test by placing some in a dish, add small increments of water, and mix with a fingertip.  After some work you should get a yellow (mine so far) to brown (commercial dextrin) slippery goo that will readily coat the dish, become tacky, then dry to a uniform film, like envelope flap glue.  Also it smells quite appetizing.  Do not allow yourself to imagine delicious underglazed donuts.
I don't have a quantified recipe yet.  Starting point was 7 units of gum arabic to 5 units of yellow dextrin, but I don't have a ratio to underglaze, or an initial dry-down factor.  All I can say now is gloss-surfaced toothpaste consistency, and that I usually add gum arabic beyond the initial amount, until it looks and feels "right", and proves in a print and transfer.
If anyone is aware of a small quantity source for the darker, more deeply pyrolyzed starch sizing/adhesive called "British gum" please let me know.  Easy to find in container loads from India, not so easy otherwise.
Experimenting with papers, in addition to half-ripe xuan previously noted, has brought good results with two papers thinner than the xuan. 
First is Yasutomo hanshi calligraphy practice paper, nearly tissue-thin, which looks like a machine glazed (MG) paper.  One side is nearly shiny, and the other is dull.  This gives good impression and transfer, and may be a better choice than xuan for curvatures.  The wet strength is sufficient to safely pull a screen print (I oven dry and the print goes very waffle-crinkly), but sponged application requires care.
Second, surprisingly, is dirt-cheap smooth (not creped) medical examining table paper (also has MG surfaces). I gave up on this immediately for hot oil intaglio transfer years ago, because it did not survive the soap sizing needed for that process.  It is just good enough, however, for this process, and I already had plenty.   More fragile than xuan or hanshi, but readily available and economical.  Results may vary.  I spoke to a converter/wholesaler some time back, and he cautioned that this paper varies more than some due to price-driven commodity sourcing.
Hanshi peels more cleanly than exam table paper; xuan peels more cleanly than hanshi.
In this round I have been using Speedball and Amaco Velvet underglazes, both with good results.  A cookie cutter, Amaco Radiant Red, and a commercial hearts screen, have given  quick cute not-identical  Valentine charms that have brought exclamations, smiles, and even tears from recipients.
 
 

Low fire white cookie previously fired twice at cone 06 for reverse side decoration experiment, fresh Speedball Royal Blue underglaze modified with CMC powder and gum arabic solution, not dried down, Keoker ready-made screen, "half-ripe" xuan paper printed smooth side. 
Underglaze transferred and fired without overglaze at cone 06, then Mayco Crystal Clear overglaze fired again at 06.  No soap in transfer, just damp sponge, dry brush, wood tool burnish.
Previous tests had color softening and running in overglaze when overglaze was applied directly after printing, so I went with two firings.  This also allows any remnant paper fibers to burn away in the underglaze firing, reducing tedium and color damage in trying to clean those off.
I feel that CMC was sufficient to give printably thickened color without dry-down of new glaze, but gum arabic added alongside CMC gave less color spread and better image thickness at printing, and better color adhesion to the ware at transfer.  By look and feel, no measurements. Toothpaste consistency with a little gloss on the surface after a minute or two rest after mixing.
Preparation from newly opened jar underglaze, printing, and transfer to bisque can likely all be handled in a one hour instructional session. 
An instructional hobby studio with commercial bisque ware, or a classroom, would need only inexpensive screens and paper, and two safe materials beyond conventional underglaze.
Tools: plastic dish and wooden craft stick for color preparation, ordinary glazed tile as printing platen, commercial prepared screen, blue masking tape, plastic scraper, sponge, brush, smooth wooden burnisher.  Screens clean ok in slop tray water soak and rub then brief running water rinse.
Size reference: 61 mm diameter.  Conforming damp decal behavior gave transfer over and onto the edges, hinted at here.

I have been experimenting, and having good results with underglaze finer-detail screen print impression and transfer with two additives: yellow dextrin (dry powder) alongside gum arabic (dry powder now rather than bottled solution).  Both ingredients are safe but are nutrient materials that could spoil if not dry.  Partial drying of the underglaze helps to reduce bleeding in the screen impression, and to get ink that stands on the paper.  The two gums help it to stand on the paper, bind to the ware, yet unbind more readily from the dampened paper.  My current guess is that gum arabic both helps standing and binding to the ware, and that dextrin both helps standing, and loosens more rapidly with dampening to facilitate transfer.
Yellow dextrin is an industrial paper and fabric sizing and adhesive.  It is available in smaller quantities from a few sources, mostly offered as a composition binder for fireworks.   The good news is that you can make your own yellow dextrin by roasting dry corn starch in the kitchen oven.  Old industrial recipes suggest around 320 F / 170 C, but I have had better results around 375 F / 190 C by uncalibrated oven dial.  I let it roast for a few hours, with interruptions, testing occasionally.
Final result should be a yellowish buff color comparable to corn flour.  Mine is a bit lighter than the commercial product, but might benefit from hotter or longer roasting.  You are breaking the starch down into something more soluble: like old-school envelope and stamp glue.  Test by placing some in a dish, add small increments of water, and mix with a fingertip.  After some work you should get a yellow (mine so far) to brown (commercial dextrin) slippery goo that will readily coat the dish, become tacky, then dry to a uniform film, like envelope flap glue.  Also it smells quite appetizing.  Do not allow yourself to imagine delicious underglazed donuts.
I don't have a quantified recipe yet.  Starting point was 7 units of gum arabic to 5 units of yellow dextrin, but I don't have a ratio to underglaze, or an initial dry-down factor.  All I can say now is gloss-surfaced toothpaste consistency, and that I usually add gum arabic beyond the initial amount, until it looks and feels "right", and proves in a print and transfer.
If anyone is aware of a small quantity source for the darker, more deeply pyrolyzed starch sizing/adhesive called "British gum" please let me know.  Easy to find in container loads from India, not so easy otherwise.
Experimenting with papers, in addition to half-ripe xuan previously noted, has brought good results with two papers thinner than the xuan. 
First is Yasutomo hanshi calligraphy practice paper, nearly tissue-thin, which looks like a machine glazed (MG) paper.  One side is nearly shiny, and the other is dull.  This gives good impression and transfer, and may be a better choice than xuan for curvatures.  The wet strength is sufficient to safely pull a screen print (I oven dry and the print goes very waffle-crinkly), but sponged application requires care.
Second, surprisingly, is dirt-cheap smooth (not creped) medical examining table paper (also has MG surfaces). I gave up on this immediately for hot oil intaglio transfer years ago, because it did not survive the soap sizing needed for that process.  It is just good enough, however, for this process, and I already had plenty.   More fragile than xuan or hanshi, but readily available and economical.  Results may vary.  I spoke to a converter/wholesaler some time back, and he cautioned that this paper varies more than some due to price-driven commodity sourcing.
Hanshi peels more cleanly than exam table paper; xuan peels more cleanly than hanshi.
In this round I have been using Speedball and Amaco Velvet underglazes, both with good results.  A cookie cutter, Amaco Radiant Red, and a commercial hearts screen, have given  quick cute not-identical  Valentine charms that have brought exclamations, smiles, and even tears from recipients.
 
 

Just letting the underglaze dry down in the open is likely the best starting point, as long as it does not get so crusty that it cannot readily be mixed back to smooth toothpaste or thicker.  That has been my challenge with oven accelerated drying.  Amaco's videos show room ambient drying in a pie tin, and no additives, and their results look good with the designs and applications shown, emphasis upon bolder designs, and printing to slabs for tiles or before forming.
CMC is an admitted shortcut for using new underglaze from the jar.  It gives a good thicker consistency and is not difficult to add in increments and mix to uniform smoothness.  Note a video of Mayco screen printing additive as a mixing example.
The detriment is that all of the water from the original formulation is still there, diluting the color/ceramics and wanting to bleed and smear them under the screen and ruining both density and delineation.  Adding CMC slows this but might be impairing print density and transfer behavior, but as pointed out, there likely already is CMC in the underglaze.  Beginning with dried-down material helps (and I have at times used both oven and vacuum evaporation to accelerate).
Adding gum arabic alongside CMC (without dry-down) seems to improve print density and transfer behavior, but a test on a commercial bisque cup still gave very poor (unusable) transfer behavior by comparison to my fresh thirsty cone 06 fired low fire white cookies.  That same cup accepted a scrap from an old commercial transfer well enough.
Commercial transfers seem often to have a faint peculiar odor, somewhere between 60s elementary school tempera paint and old gym socks.  They have excellent density in the print, good release behavior from the paper, and better tenacity upon transfer.  That odor sparks alchemical intrigue, from which I will experiment.  Whatever's in there is probably less expensive than gum arabic, and works better.

The Amaco videos are very worthwhile.  I located an image on a commercial rubber stamp that I wanted on holiday decorations, and stamped that carefully into my fresh slab.  After bisque firing, I did sort of Mishima with glaze and a tiny brush into the impressed image.  I did this with convenient sloppiness, then after drying, cleaned it up by scraping and cloth rubbing, then paint and tip-in background color. I found that it was difficult to gauge stamp pressure and depth with the wood block mounted stamp, so I transfer molded the stamp twice: soft urethane negative from the stamp, then hard urethane positive from that, then trim to an outline that allows better visibility and feel when stamping.  After a couple of practice tries, I was astounded to discover the fine detail that was in the original stamp and carried through the transfer mold steps, then into the clay, that was opened up and delineated by careful scraping, and showed clearly in the final fired image.  Stamp was sold as 1.75 inch: small with fine details.
I added a photo of one.  Lighting here is tricky: the color is impressed, not raised.  Original commercial rubber stamp design is copyright Snigglesloth.
 

Low fire white cookie previously fired twice at cone 06 for reverse side decoration experiment, fresh Speedball Royal Blue underglaze modified with CMC powder and gum arabic solution, not dried down, Keoker ready-made screen, "half-ripe" xuan paper printed smooth side. 
Underglaze transferred and fired without overglaze at cone 06, then Mayco Crystal Clear overglaze fired again at 06.  No soap in transfer, just damp sponge, dry brush, wood tool burnish.
Previous tests had color softening and running in overglaze when overglaze was applied directly after printing, so I went with two firings.  This also allows any remnant paper fibers to burn away in the underglaze firing, reducing tedium and color damage in trying to clean those off.
I feel that CMC was sufficient to give printably thickened color without dry-down of new glaze, but gum arabic added alongside CMC gave less color spread and better image thickness at printing, and better color adhesion to the ware at transfer.  By look and feel, no measurements. Toothpaste consistency with a little gloss on the surface after a minute or two rest after mixing.
Preparation from newly opened jar underglaze, printing, and transfer to bisque can likely all be handled in a one hour instructional session. 
An instructional hobby studio with commercial bisque ware, or a classroom, would need only inexpensive screens and paper, and two safe materials beyond conventional underglaze.
Tools: plastic dish and wooden craft stick for color preparation, ordinary glazed tile as printing platen, commercial prepared screen, blue masking tape, plastic scraper, sponge, brush, smooth wooden burnisher.  Screens clean ok in slop tray water soak and rub then brief running water rinse.
Size reference: 61 mm diameter.  Conforming damp decal behavior gave transfer over and onto the edges, hinted at here.

The Amaco videos are very worthwhile.  I located an image on a commercial rubber stamp that I wanted on holiday decorations, and stamped that carefully into my fresh slab.  After bisque firing, I did sort of Mishima with glaze and a tiny brush into the impressed image.  I did this with convenient sloppiness, then after drying, cleaned it up by scraping and cloth rubbing, then paint and tip-in background color. I found that it was difficult to gauge stamp pressure and depth with the wood block mounted stamp, so I transfer molded the stamp twice: soft urethane negative from the stamp, then hard urethane positive from that, then trim to an outline that allows better visibility and feel when stamping.  After a couple of practice tries, I was astounded to discover the fine detail that was in the original stamp and carried through the transfer mold steps, then into the clay, that was opened up and delineated by careful scraping, and showed clearly in the final fired image.  Stamp was sold as 1.75 inch: small with fine details.
I added a photo of one.  Lighting here is tricky: the color is impressed, not raised.  Original commercial rubber stamp design is copyright Snigglesloth.
 

A year late to this, but I experimented with carbon process back in the 70s, both with Hanfstaengl black carbon tissue and with self-made materials.  I had some success in placing gelatin/pigment images on glass, that showed some promise of at least limited continuous tone density range.  I used glass because Kodak glass slide covers were readily available and accepted coatings.  I used one or another hardness of photo gelatin, and dry pigments from the art store. 
(I have had good results in ceramics with selected Gamblin dry pigments: Cr green, Co blue, Fe/Mn umbers and siennas, as dry press body colorants and in hot oil intaglio transfer inks.) 
Recall that in continuous tone carbon, your range of image density is created by range of pigmented film thickness, the image will harden from the exposure lamp side inwards, and that you need ultraviolet (I used a now-contraband 60s suntan mercury vapor suntan bulb).  You are running a race between colorant density needed to form the image, and colorant+frit... density absorbing and scattering the exposure light against hardening more of the carrier.
It's tempting to try this again, but I feel that it is no longer responsible to flush dichromate, even where it might not be directly illegal.  Oh yeah: also the formaldehyde for hardening.  Diazos aren't necessarily super safe, but at least they're easy to destroy.

A year late to this, but I experimented with carbon process back in the 70s, both with Hanfstaengl black carbon tissue and with self-made materials.  I had some success in placing gelatin/pigment images on glass, that showed some promise of at least limited continuous tone density range.  I used glass because Kodak glass slide covers were readily available and accepted coatings.  I used one or another hardness of photo gelatin, and dry pigments from the art store. 
(I have had good results in ceramics with selected Gamblin dry pigments: Cr green, Co blue, Fe/Mn umbers and siennas, as dry press body colorants and in hot oil intaglio transfer inks.) 
Recall that in continuous tone carbon, your range of image density is created by range of pigmented film thickness, the image will harden from the exposure lamp side inwards, and that you need ultraviolet (I used a now-contraband 60s suntan mercury vapor suntan bulb).  You are running a race between colorant density needed to form the image, and colorant+frit... density absorbing and scattering the exposure light against hardening more of the carrier.
It's tempting to try this again, but I feel that it is no longer responsible to flush dichromate, even where it might not be directly illegal.  Oh yeah: also the formaldehyde for hardening.  Diazos aren't necessarily super safe, but at least they're easy to destroy.

A year late to this, but I experimented with carbon process back in the 70s, both with Hanfstaengl black carbon tissue and with self-made materials.  I had some success in placing gelatin/pigment images on glass, that showed some promise of at least limited continuous tone density range.  I used glass because Kodak glass slide covers were readily available and accepted coatings.  I used one or another hardness of photo gelatin, and dry pigments from the art store. 
(I have had good results in ceramics with selected Gamblin dry pigments: Cr green, Co blue, Fe/Mn umbers and siennas, as dry press body colorants and in hot oil intaglio transfer inks.) 
Recall that in continuous tone carbon, your range of image density is created by range of pigmented film thickness, the image will harden from the exposure lamp side inwards, and that you need ultraviolet (I used a now-contraband 60s suntan mercury vapor suntan bulb).  You are running a race between colorant density needed to form the image, and colorant+frit... density absorbing and scattering the exposure light against hardening more of the carrier.
It's tempting to try this again, but I feel that it is no longer responsible to flush dichromate, even where it might not be directly illegal.  Oh yeah: also the formaldehyde for hardening.  Diazos aren't necessarily super safe, but at least they're easy to destroy.

Received this from Amaco after inquiry. Easy breezy to roll on thickened underglaze (after drying somewhat), as several mentioned here on the forum. Easy to clean up, too. Good tip on attaching plastic wrap on freshly printed slab when constructing to avoid smearing.
https://www.amaco.com/clay_how_tos/314
 

Left example is one of Mayco Stroke and Coat purples, right is Speedball purple, both with Mayco Crystal Clear overglaze.  62 mm diameter after firing.  Colors were dried down, and modified with gum arabic solution as previously mentioned.  Ready patterned screens were probably Keoker.  "Half-ripe" xuan roll paper.  I sponge on the dried transfer print, then brush with a soap solution, and burnish with a wooden tool before peeling.  Soap solution brushing is a habit from earlier hot oil/intaglio fine line work with soap-sized tissue (soap sizing the tissue before printing is necessary there, but counterproductive for aqueous glazes), and may not be essential.  Look for the color to go more white under the paper surface as a partial clue to adhered transfer, not as reliable an indication as with commercial transfers, but useful.  Clay Planet Low Fire White cone 04 bisque then 04 or 06 glaze.  I have also had good results on Texas Blackjack clay (dark gray in the block, fires white).  Note how the Mayco purple does not develop as strong a line density, but gives a pleasantly softened line under the clear glaze.

Left example is one of Mayco Stroke and Coat purples, right is Speedball purple, both with Mayco Crystal Clear overglaze.  62 mm diameter after firing.  Colors were dried down, and modified with gum arabic solution as previously mentioned.  Ready patterned screens were probably Keoker.  "Half-ripe" xuan roll paper.  I sponge on the dried transfer print, then brush with a soap solution, and burnish with a wooden tool before peeling.  Soap solution brushing is a habit from earlier hot oil/intaglio fine line work with soap-sized tissue (soap sizing the tissue before printing is necessary there, but counterproductive for aqueous glazes), and may not be essential.  Look for the color to go more white under the paper surface as a partial clue to adhered transfer, not as reliable an indication as with commercial transfers, but useful.  Clay Planet Low Fire White cone 04 bisque then 04 or 06 glaze.  I have also had good results on Texas Blackjack clay (dark gray in the block, fires white).  Note how the Mayco purple does not develop as strong a line density, but gives a pleasantly softened line under the clear glaze.