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Magnolia Mud Research

Member Since 28 May 2016
Offline Last Active Today, 07:17 PM
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#123058 Glazing Lidded Pots

Posted by Magnolia Mud Research on 01 March 2017 - 10:54 AM

I use alumina in wax, similar recipe to Marcia's except I eyeball the amounts, on all lids.  Generally on grogged clay bodies the surfaces are rough enough not to seal, but with low grog clay bodies and/or burnished  galleries there can be some adhesion between the lid and the gallery.  The alumina-wax is a reasonable countermeasure.

 

Kiln wash is not recommended as an alternative because it often contains both kaolin and silica, both of which are more likely to sinter together and adhere to the clay body.  Alumina, by itself, does not.
 
LT




#122989 Some Questions About Lidded Jars

Posted by Magnolia Mud Research on 27 February 2017 - 03:14 PM

re the question on fired volume relative to wet volume for mugs:

If you know your percent shrinkage for your clay body, you can estimate the volume shrinkage for a mug by using three times the linear shrinkage.  ie, if your mug made from a lump of clay holds 100 cc when wet and the shrinkage is 10 pct for that clay body, then you mug will hold about 70 cc after it is fired. 

[There are some second and third order terms that could be considered, including the phase of the moon and how many grapes you had for breakfast last friday, but they are all quite small.]
 

LT




#122981 Glazing

Posted by Magnolia Mud Research on 27 February 2017 - 01:39 PM

Ron,

 

After the first few forays into glazing in my first semester of ceramics I was introduced into test tiles and what they could do for me.  We had about 10 glazes in the studio so I made a large tile and marked off 100 squares on the tile - think chess board - and created a grid with each glaze having a row and a column.  Glazes were applied first to the rows and then to the columns.  Each square in the grid had a first coat of one glaze and a second coat of another glaze.  With one firing, I got  100 samples of how the 10 glazes interacted with each other and individuality.  That was the most useful glaze exercise that semester.  Since then I have used the same idea for the glazes I use regularly and for glazes I want to explore.  I have used a variety of 'test' pieces - shot cups to large bowls to just a glob of clay.  If I keep the test pieces small, they fit into the kiln easily in the 'shadows' of larger pieces. 
 

Susan Peterson's textbook "The Art and Craft of Clay" explains the technique plus images of the grid.  It is the best reference for understanding 'glazing' that I have encountered.

LT




#122949 Number Of Firings

Posted by Magnolia Mud Research on 26 February 2017 - 08:08 PM

Yes.  if the solids in a spoon full of wet glaze dries to one oz  and you need three spoons worth of glaze you would use a 0.005 x 3 oz of silicon carbide.  (or about 0.43 grams )

 

Min's procedure is also reasonable approach.   I seldom use commercial glazes, so I have no insights on the solids to liquid ratio for them. 

 

LT




#122875 Slip Inlay On Groggy Body

Posted by Magnolia Mud Research on 24 February 2017 - 05:38 PM

I suggest that you apply several thin layers of grog-free white clay body over the leather hard stoneware; and after the sheen is gone from the slip, compress the slip layers with a roller or soft rib.  This will provide a grog-free surface to carve on. The compressing step forces the slip to bind tightly to the stoneware and reduces the tendency to form surface cracks when drying, especially if you use a porcelain slip. 

 

Think of the slip layer as a 'gesso' for a clay canvas.

 

The technique works great for pet headstones with crisply carved decorations and lettering on a sturdy body. 
 
LT




#122767 Number Of Firings

Posted by Magnolia Mud Research on 22 February 2017 - 07:35 PM

I would aim to have the bisque and crater glaze fired at the same temperature, say bisque to cone 05.  Then you could fire the crater glazed items along with the bisque items. 
 
I also would try firing the crater glaze on a test object to cone 6 and see what happens. 
 
LT




#122471 Why Didn't Someone Tell Me About Paperclay!?!

Posted by Magnolia Mud Research on 18 February 2017 - 11:07 AM

Jed,

The answer is yes,

but:
 
And if the lint is all cotton, the performance will be similar to use of paper. 
 
The lint fibers will be a lot longer, and this could either be a benefit or could be a problem depending on the forms, techniques, etc.
 
If the lint is synthetic fiber, you will not get the same benefit of moisture movement via the cellulose fibers (in paper)  during drying and the 'burn out' gases will probably smell different and probably will take require a different temperature for complete burnout.
 
LT




#122450 Adding A Touch Of Gerstley Borate?

Posted by Magnolia Mud Research on 17 February 2017 - 05:24 PM

My approach would depend on whether I was trying to create from scratch a glaze that included a significant amount of GB or if I was trying to modify an existing glaze by  adding or substituting GB to the glaze.
 

If it were a from scratch point of view, I would use the Currie Grid approach illustrated by Joel.  This would give me quick look at the landscape and allow me to narrow down the region I wanted to explore with narrow range line blends.
 

If it were the modify an existing glaze to just add GB, I would start with a set of line blends between 100 % existing glaze and 100 % GB.  I would use 9 steps. Because I would mix a big batch of the 100% ends and volumetrically mix to form the middle and then split the halves into halves and the half-halves into half, etc., or just measure by thimble measures to produce an even spread of ratio of EG (existing glaze) and GB. 
 

The really difficult decisions are what properties of the new glaze are you going to evaluate and how will you measure the results.  My inclinations drive me to just do a coarse screening experiment and after the fired test tiles are available follow what looks exciting. 
 

I fire at cone 10, and GB produces a nice clear glaze on stoneware. I have not tried it on porcelain.  I have no data or speculation on the leaching or fit since I was experimenting for decorative effects on sculptural objects where leaching or fit was not an important constraint.   I do recall that GB can show up in a wide range of glazes from Raku to cone 10.  It is a reasonable alternate source of calcium and boron oxides without using frits.  It does change the rheology of the glaze slurry relative to glazes without GB, but you will know that going in and can avoid the 'knee-########' responses to rheology fluctuations.
 
LT


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#122258 Torus Resources

Posted by Magnolia Mud Research on 13 February 2017 - 06:19 PM

Is the 'flask' discussed in this document what you are aiming for?  http://resources.met...l_v_18_1983.pdf

 

There are several ways to create one.

 

LT




#122108 Crater Slip

Posted by Magnolia Mud Research on 11 February 2017 - 12:22 PM

I have use corn meal in porcelain slip to produce 'craters' when fired.  It was applied with a brush or spatula.  If you used large sized needles from veterinarian syringes probably would work for semi-fine lines.  I got the idea from a book on Lucie Rie's work.  One of her signature series was a white clay body with pockmarks all over - supposedly due to rice added to the surface layer.

 

LT




#121847 Vertical Heat Clearance

Posted by Magnolia Mud Research on 06 February 2017 - 06:34 PM

To get good ventilation to a space, you must have an entry and an exit, one is for bringing the fresh air in and the other is for getting the non-fresh air out.  You will not get ventilation from only one opening, even if that opening has a fan!   
 
LT




#121698 Cheap Wax And Methane Musings

Posted by Magnolia Mud Research on 03 February 2017 - 08:44 PM

Joel,

Once upon a time, I also found that wax did not work for me.  I switched to shellac.  It flows nicely, dries quickly, smells good, is removable with denatured alcohol, and the brushes clean quickly with denatured alcohol.  It does not cause the glaze to 'bead up' as well as wax, but the glaze does wash off easily with a wet sponge.  If applied with a thick coat to produce a smooth surface, the glaze wipes off easier as the grains of glaze material don't get caught in the holes of the bisque.  Fill up the holes with something that burns out is the main function of the resist.  Olive oil repels water, but is not a useful resist as the glaze particles still get trapped in the pores of the bisque.
 
I no longer use it because I redesigned my pots to more easily allow me to not get glaze on the parts that should not be glazed, foot rings, lids, etc.  Much of my exterior decoration is now done with stains, applied clay washes, or just left bare. When necessary to dip the whole pot into glaze, I first wet the pot with water to saturate the areas that should be glaze free. Very little glaze 'sticks' there and wiping is adequate.  Eliminating the steps of adding resist, cleaning the bottom, etc.  made glazing less of a chore and saves time.

 

LT




#121587 Firing Earthenware Jugs - Basic Questions

Posted by Magnolia Mud Research on 02 February 2017 - 10:58 AM

Oly

 

For the first few years in ceramics I used a white Texas earthen ware that was typically fired ~ cone 04, but the studio fired it to cone 3 in oxidation.  It was tight, fully mature, and did not slump or warp, especially on mugs.  I now use it for a decorative glaze accent at cone 10 reduction.

 

Make some prototype mugs and fire them without glaze and see what happens with the white earthenware you have.  You will find a firing temperature that will produce good water tight mugs.  Then develop a glaze that works at that temperature.  Use that glaze as a base and make mugs. 

 

LT


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#121440 Calgon Bath Bead Mother Of Pearl Glaze Recipe

Posted by Magnolia Mud Research on 29 January 2017 - 04:59 PM

From the Leaman Pottery post :
"... I ... learned about using Calgon Bath Beads to achieve a very lustery Mother of Pearl effect .... . Does anyone know about this glazing method"?

 

My conclusion is  that the Calgon beads were added as a major glaze ingredient, not as a deflocculant.
 
Dick White posted: "Prior the mid-1980s, the active ingredient in Calgon water softener was sodium hexametaphosphate."
 
If the Calgon beads were a major component in the glaze you should look for a commercial source of sodium hexametaphosphate (SHMP) [(NaPO3)6].
 
I regularly use Trisodium phosphate (TSP) [(Na3PO4)(H2O)12] as a glaze ingredient to add phosphorus to the melt -- up to 25 %wt in one glaze recipe.  It is available as a paint remover and cleanser at most hardware, paint, and some grocery stores.

 

 

As far as the glaze is concerned the difference between TSP and SHMP is in the sodium to phosphorus ratio.  TSP has Na/P of 3 while SHMP has Na/P of 1.  Phosphorus oxide is a network former (glass former) and also promotes the Mother of pearl (opalescence)  effect in the glaze. The sodium that comes along with the phosphate is just more (R2O) 'flux' in the glaze.

 

If I were going to try to produce glaze with an "MoP luster' glaze, I would start with a clear glaze I already have experience with and make a line blend test using  say 2, 4, 8, 12, 16 pct phosphate to the recipe and see what happens.  Assume the test glazes will run (probably won't) and protect the kiln shelf just in case!

 
Concerning the floc-defloc:
Both materials are water soluble and either can change the glaze slurry properties when used in 'trace' amounts.  When  TSP or SHMP is used as a significant ingredient to the glaze recipe proper, the concentrations are high enough that the floc-defloc issues are irrelevant. 
 

 
LT




#121307 "fitting" Glaze Shivers When Applied Thin?

Posted by Magnolia Mud Research on 27 January 2017 - 11:48 AM

How thick are the rims of the bowls and cups that are shivering?  Also how sharp are the 'corners' between the wall surface and the rim surface?  I often see work that has problems due to not enough surface area to hold on to the glaze layer. The actual failure is in the clay body, not in the glaze. 

 

A thick layer of strong glaze can often cover up a structural design issue.

 

LT