Hulk
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Could be the glaze layer at the rim is thinner.
Could be the rims were worked more at finishing, hence sand and/or grog are more exposed.
Could be a combination of both?Reglazing and refiring, hard to say; some have luck with that, some don't.
Any road, building up a slightly thicker layer of glaze at the rim might help.
Using glaze that doesn't move/sag much might also help.I'm curious if the problem mugs are together in the kiln, perhaps a hotter area?
I've used a buff stoneware that weeps tiny droplets when fired hot. The droplets stick but can be scraped off bare clay (e.g. the foot ring). The droplets will be hidden in the glaze layer, where the glaze is thick enough, else there's a gritty feel.
It's annoying! ...haven't seen it in any other clay, just the one buff stoneware. -
Three; white, red, and buff with speckles stoneware.
The first two are mined, processed, and sold by a local (Sacramento) company; the speckled buff is a Laguna product that they carry.
I'd been working on fitting my liner glaze to white stoneware, then tried a different clay, voila! ...haven't changed the liner glaze formulation since, although I did switch clays.
I like each color - and the glaze response to each - too much to give any up just yet.
Each is the "best of" so far.
Prior white stoneware got me working on low COE liner glaze, were not as plastic, had higher rate of "off-gassing large particle defect" and cost more to get, being further away.
Prior red stoneware, not as plastic, narrower glaze firing range (much), higher rate of particle defect, poor drying behavior, cost more to get.
Prior buff stoneware, narrower glaze firing range, cost more to get. -
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Hi Pye,
The marking inside the bowl is red slip, added shortly after trimming - whilst the ware is still damp*.
I'd blunged up some red stoneware clay (with the Studio blender, a thrift shop special!) with water, then ran the slurry through the 80 mesh sieve to remove the sand and other bits. A few cups goes a long way.I've brushed the slip on the outside of wares, using the wheel, then carved design/pattern after the slip had dried some.
On the inside, I've done some stippling, like the one depicted above, dabbing the slip brush as the ware turns on the wheel. After bisque, any lumpy/rough parts sand away easily. Some of the slip "disappears" in the glaze - the effect is muted, somewhat, by the glaze and glaze firing...
Liner glaze, I'd decided, early on, to stay away from metallic colorants, even though there are stable/safe/tested recipes "out there" from trusted sources. For design underneath liner glaze, I believe the slip is ok, and underglaze should be fine as well, also some small droplets of (stable) colored glaze underneath or on top.
Commitment to utility! Tough, easy to clean, doesn't mark, un-crazed, well behaved (applies well) glaze as a liner.My liner is clear-ish. Over red, black, or dark brown clay, the Zircopax - at 2%, a translucent white - shows up.
Over white clay, it appears to be clear (but it ain't!).
The Zircopax to lower COE a bit, add some toughness, and reduce bubbles.
Zircopax (digitalfire.com)
Liner Glaze (digitalfire.com)*but stiff enough to take on some more moisture - from the slip.
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Hi Byrd,
Welcome to the Forum!
Good question.
Making it through a fast bisque with no damage, that's a win - if the ware went in damp, a quick ramp up past 212°F could be problematic (pro BOOM atic)!
From there, thinner ware should be happier with a short bisque than thicker ware, same for "cleaner" clay, for one of the objectives is to burn out organics/combustibles, which takes longer for thicker ware, and can take longer for "dirtier" clay.If the wares are thick, if you're using red, brown, or black clay, a more thorough bisque might help - testing will tell, hard to say...
My typical bisque runs about eight hours, however, I'm ramping up to about 200°F the night before, then skipping the initial warm up (to drive off moisture) the next day. I hold at about 1500°F for at least half an hour, which I've found helps burn out stubborn gassy bits, direct kiln vent running throughout - ample oxygen for the burn out.
See second paragraph:
Bisque (digitalfire.com)- Pyewackette and Rae Reich
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Typical direct vent setup* draws a tiny stream of kiln atmosphere from the kiln, which is mixed with much more ambient air in the "plenum" - a box/shape that sits tight against the bottom of the kiln, has the exhaust hose connected to it, and vent holes to draw ambient air. Adjustable vents in the plenum, a decided plus, imo.
* Hence, allowance must be made for "make up" air to enter the space, as the fan pulls (and pushes) dozens of cubic feet per minute out of the room! *
In my (limited) experience, direct vent setups get a lot of the fumes, but not all, which may not be a concern for a small kiln...
*like the setups marketed by many kiln vendors
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Look also for the glaze layer cracking as it dries on the piece - some glazes will, err, can run together when they melt, others pull apart along the crack lines.
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We try to maintain and repair all we can, excepting where it's warrantee or insurance work, beyond our ability/experience, just too big a job, and/or stuff we don't want to do.
First kiln was a 1983 all manual.
I wasn't hep on how to safely work on the main panel with the solar, so hired a contractor to install wiring for the kiln (ouch, $$$).
Disassemble, move, assemble, setup, we did all that.
Direct vent, overhead vent, we designed and built.Second kiln, brand new automated - having learned somewhat about solar when we upgraded the wiring to our son's well house - we ran the wiring this time, and same "we did that" as the first kiln, re-using the direct vent*.
The kiln is running a glaze fire now (first one!); it has one bisque fire under its belt.Certainly, it's possible I'll need help repairing/maintaining the new kiln, however, it looks straightforward; plan is we'll do it.
We call for help when we need it, e.g. going up on the roof to clean out the gutters, I'm not doing that.
Building the wall for the Studio, running wiring for lights, plugs, and dedicated circuit for the mini-split, we'll do all that; the sheet rock, top, texture, paint, that too; hanging and casing the door, baseboard, all that.
The example in our family was very much do it yourself, do the maintenance and repair. I'm curious (still!), cheap, and need to get focused into stuff to stay busy. Along with "saving money" by diy, one has control of the quality.
We had access to tools from the start. My brother and I took everything apart.
I worked in several trades.
...was just reflecting t'other day on how much learning is associated with mistakes, yes, all along and into the present, no doubt more in the future.
...for example, when closing the kiln wiring/control box, it is possible to arrange the wires so that in closing, wires push each other unconnected. Ah.
... " ", I'd forgotten the glaze that beads up on the waxed surface can drip - catch them before turning the ware over! Ah.
*The overhead vent to be re-purposed as a dust vent, for glaze prep.
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Here the outside (upside for lids) has been dipped.
Inverted, the glaze goes up the inside as the trapped air is compressed, however, it doesn't stick, for the liner is waxed from the lip to about 3/4" down.
After the dip, an initial swipe with a sponge* to catch the biggest drops of glaze beaded up on the wax prevents them from sliding down the wax when the pot is righted, there.
Then, any remaining droplets are easily caught, no hurry, for they are beaded up on the wax.For the dip, I'm lowering these (careful not to "burp" any air out!) smoothly to full depth, retrieving to the upper limit of chatter marking, then lowering to the lower limit of the chatter marks (not all the way to the foot!) afore withdrawing the piece - steady, not too fast! - shake, shake, run the drip around, sponge the big droplets off the wax, right the piece, etc.
Varying the speed of withdrawal can make for interesting banding, particularly with transparent and semi-transparent glazes...
Upside down dip, simple way to control glaze thickness - thinner near the foot, thicker near the lip.Where the glaze is "watery" (for my glazes, specific gravity 1.41 to 1.46, depending on the glaze) enough, I don't have to hurry to prevent too thick a layer, and, And, where the glaze is "gel" enough**, it does not run, drip, sag.
Waxing, cutting and cleaning for the sharp boundary at the lip is a bit of trouble, however, I like the look.
I'm taping off the foot, as I like the clean sharp edge there too. The tape provides a handle as well. I'm removing the tape while the glaze is still moist - less dust.
The area within the foot ring, I'm using a squirt bottle, level with a wet finger, sponge* away any oops, done.
*Where a big sponge is too much, cut the "right" size and shape from a big'n! ...still thanking Bill Van Gilder for that tip, thanks Bill!
** per often mentioned (by me!) adjust that thixotropy!
See Tony Hansen's articles on dipping glaze, thixotropy, etc. and Thixotropy and How to Gel a Ceramic Glaze (digitalfire.com)- Pyewackette and Rae Reich
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Amy Palatnick video clips come up in FB...
I like!
Amy Palatnick - YouTube -
I put the clay pad on a bat* when using unholy bats*!
*likely the practice is very frown worthy...
*plaster and oversized
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Hi Gillespie, welcome to the Forum!
My first kiln was fully manual*.
I used cones. At first, I watched the cones through the peep holes (wearing kiln glasses against harmful rays and flying bits). Later, I relied on the pyrometer, and checked cone packs afterward. Keeping detailed notes really helps - time, temp, observations, results.I'd run up to about 200°F the night before, all peeps left open. The next day, all three switches on high, then toggle the switches to hold at 1500°F for an hour**, then full speed to cone 04, then off. I'd fitted the kiln with a downdraft vent; for bisque, I just leave the fan on until it's cooled to 1400...
That's what worked for me, ymmv
The portable pyrometer has been very worthwhile, imo.
*three high/medium/low switches and a sitter.
I see the sitter as a safety backup, never depended on it.**holding at 1500 seems to help, particularly for buff, red, and black clays...
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Good questions.
I don't have answers, will share an observation: the tin-chrome red glaze I'm using* picks up blue flecks, I'm guessing from neighboring pots, however, some of the flecking could have been from the kiln**.
Sometimes there's more blue flecks on surfaces facing upward-ish, sometimes more on one side than the others...My glaze loads typically have a lot of blue in thar, a semi-transparent blue, a variegated blue (with rutile), and a light blue; all use cobalt carbonate.
*got the recipe from local JC ceramic lab (matches "Chrome Red" from John Britt's book)
**my guess is that the same will happen in my brand-new kiln, tbd.
The old kiln had seen almost thirty years of service before it came to me! The prior owner definitely used blue glazes... -
More reading:
Very paranoid about Silicosis - Studio Operations and Making Work - Ceramic Arts Daily Community
Silica Dust Exposure - Studio Operations and Making Work - Ceramic Arts Daily Community
Can air purifiers remove silica dust from my Ceramic Studio - Studio Operations and Making Work - Ceramic Arts Daily Community|
Dust Collection For Small Studio - Clay and Glaze Chemistry - Ceramic Arts Daily Community
Toxicity (digitalfire.com)Dedicated Studio shoes/sandals, no tracking clay into the house!
For if/when clay gets on clothes, have a few clean sets handy in the Studio.
Change rags when there's any dry clay on thar, bag or drown in water, along with dusty clothing! ...else, wet that rag.
Wipe down clay smear/bits inside the clay bags with a big ol' sponge, then spray a mist of water in thar before closing up the bag.
Dry clay on plastic sheeting/bags -> instant dust!
Handle the dried out empty clay bags outside, away from the Studio (clean inside and out, save for reclaim!).Some forum regulars are using air filtration systems, also centralized vacuums (where the exhaust is routed outside/away).
My overhead kiln vent doubles as a glaze mixing station fan.
I'm handling the glaze material outside, away from the Studio door - repacking from the sacks and bags into lidded containers - then hosing the area down later.
Find a P100 (or equivalent) dust mask/respirator that fits you well and wear it when doing dust things.
Check/clean surfaces regularly. Note where dust accumulates, and how much - that's why I believe wedging and trimming are what generates dust in my Studio.
How else can one assess the dusty-ness of the working space?
Heh, I've posed this question several times over the last five years or so...- Rae Reich, Pres, Pyewackette and 3 others
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Hi Pot, Welcome to the Forum!
Good question. I'll circle back and post links to further reading later...
Meanwhile, I work in a single car garage space (previous Studio was also a single garage space!), which does have ventilation options, however, much of the year is rather hot, else chilly.
I try to keep after the floor with a wet mop - an actual commercial bucket, wringer and mop. Having the floor accessible helps there. The mop is handy for cleaning off shoes/sandals as well - don't track it around!
In general, any dry clay - bits, pieces, splatter, slip - can easily become dust. Hence, I'm looking to keep dry clay to a minimum, wipe off the work surfaces, tools, wheel. No waving cloth about that has dry clay embedded in (rags, clothing, the dreaded canvas, ugh).
The only dry clay I want to see is greenware awaiting first fire (on shelves, out of the way and protected), and clay to be reclaimed (stored away).I'm seeing the wedging station being a dust source, also trimming at the wheel.
There are strategies for minimizing those dusts, tbc.The typical dust generators I see are:
stepping on clay that's on the floor
dry clay, slip, glaze, etc. that's disturbed and flies into the air
airborne dust that's settled, then re-launched, repeat, repeat...It's nice to have ventilation, however, I try not to roll up the door or open the window if there's any dust to be kicked up by moving air - clean up time.
Best case, my Studio is relatively dust free when I start a session, then I've cleaned up at the end for next time.- Pyewackette, Pres and Rae Reich
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Likely "Search Engine Optimization"
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Pulled handles came up in t'other thread.
Much as I'd like to practice pulling several from a large handful, I've a hard time supporting much in my left where the right can do the other part, and reversed hands is worse!
I'll roll between sixty to ninety grams of clay (for the usual wares - more for a big pitcher, teapot, etc.) around on my wedging board to dry it a bit, then roll it into a tapered carrot shape before pulling it.
It's rather cheating?
I'm going for a tapered roll that's close to the final I want, with a flare at the big end to hold on to, then hang it from whilst it firms up.
It works for me! ...starting out, I'd make/pull two or three for each ware, and pick the "best" one. Hmm, that went away a while ago... -
A small amount of Nerd's reclaim mix makes a noticeable difference in four to five gallons of reclaim slurry, in my experience.
I'd tried between a quarter to third cup of the recommended mixture, eight parts of silica, one part OM4 ball clay, one part feldspar.
Now I'll use it if the reclaim contains significant amounts of re-reclaim and/or re-re-claim... -
We had some big scraps of material, half inch and three quarter inch thick* that I made bats out of.
Not sure what brand/type of material - it's a particle board, or fiberboard of some sort, but the bits/particles are very small.Any road, so averse am I to $pending on bats, I cut and drilled the material into rounds same size as the wheel head, also squares (with rounded corners) big enough to catch the bat pins in diagonal corners, then treated them with oil based stain, several times, allowed for thorough drying (a few weeks in the sun), and a final coat of polyurethane.
add: might've been oil bourne varnish, idkIf there's a next time, I'll skip the poly - it's great until it starts to fail. Where the poly has completely worn away, the bats are just starting to absorb moisture and swell a bit - time to dry thoroughly and re-treat with oil stain. ...or just start using the other side!
Over five years later, they are holding up fairly well.
I have two black plastic bats that are ok, however, they do flex a tiny bit, which is enough to distort ware (easily fixed, yes - still a bit annoying tho').
The Speedball bat is rigid but expensive. I didn't like the blind holes (easily remedied).The HardiPlank bats may answer!
add: I want to try coating them, then comparing to sanded/polished ones left uncoated ...not decided on what to try, something that sticks and wears really well, maybe two part epoxy paint.
*I really like the thick ones. Although it looks like water/slip would sling over the lip of the splash pan, as the surface is that much higher, it doesn't, miracle!
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I still want gas!
Fire, flame, fun, go!However, not practically possible at our previous home, same here at our new/current home.
The electric gets the job done. I love opening the kiln after a firing!
One of the "important" things was either existing solar or suitable for solar.
We sized the system with electric car, seven cubic foot electric kiln, 3/4 ton mini-split (Studio) and second EV (down the line) in mind.
That help$.I'm liking the Quad elements.
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Try "benchtop buffer" or somewhat like for a search string, e.g.
There are several sizes, powers, options "out there!"
The unit should be securely fastened (unlike the image above!), and, And, careful be, against any wrap up scenarios, also pinch points...
- Jason Schiedel and PeterH
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Interesting!
My guess, bisqued to a higher cone may (almost certainly) have some influence on the final product*, however, I'm not seeing how it would influence the glaze firing's heat work.
My second guess, that twenty minute hold once 2200°F is achieved would push to the next cone; what I don't get is why it hadn't previously...
*glaze thickness comes to mind, however, likely you'd already adjusted for that!
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A bench unit with a large and wide buffer on one side, a narrow and small on t'other might serve - and swapping out the buffing wheels may offer more options, e.g. try searching "v edge buffing wheel" or something like...
Trying for Cone 1 glossy/satin white
in Clay and Glaze Chemistry
Posted
Tony Hansen has published a few articles on low fire glazes, e.g.
G1916Q (digitalfire.com)