Need Tips On Drying Racks & Procedures

[oldlady]

stellaria, i do not understand why you think drywall is weak.  perhaps you use a lot of water in making pots, i know there are people who do that.  or maybe your drywall is too thin.  mine is 1/2 inch or 5/8 inch thick.  cannot imagine losing a shelf of work because of weak drywall.  mine MIGHT show some signs of dampness after holding 20 butterdishes overnight but i just slide them off to a dry sheet and let the other one stand against the wall to dry thoroughly. been using the same ones for more than 15 years, sliding them in and out of bakers racks like drawers.

[Mark C.]

As far as using plastic-I have a large plastic tub in studio where large pieces are stored (I save these from recycled use of anything that comes in a large bag-some are the  dry cleaning type on cloths -other come around large items like outboards or car parts whatever you can find) I cut them open so they are sheets. These last for many years coving work and on a daily basis go on and off work. Some are thin and some are thicker-If the are real thick and large bags I use them to wrap my extruders whole on the wall to keep them from drying out. This for me works best as I do to muck extruder work to put a bag over my clay each time the barrel is loaded-like yeaterday when I shot 4 barrels of soap dishes. These bags are free and get reused hundreds of times. As I said I cover any work that has an attachment for one night then let it dry uncovered. The exception is sculpture or teapots.

 

Mark

[Barb Z]

I have two drying procedures, one for thrown pieces, and one for slab-formed.

 

The thrown pieces go onto a ware board (plywood), sit until I can turn them over, sit again until they are trimable, and once trimmed, they go on wall shelves to dry. If I want them to dry slowly, they go in a damp-cupboard between throwing and trimming. Otherwise they sit out in the studio. If I attach a handle, the piece gets bagged (with twist-tie) for 8 hours, then put out to dry.

 

Slab work is much different, and much more vulnerable to drafts. I make plates and trays over a hump-mold, and put them and the mold in the damp-cupboard until they are stiff enough to hold their shape if turned upright. I then turn them upright on pieces of wallboard, and set them on rolling wire racks such as you have in the pictures. I wrap the 4 sides of the rack with a plastic drop-cloth, held on with sections of split pipe insulation. The top and the bottom are open, so there is circulation from my heated floor, but no drafts from one side. They dry in 3 to 4 days, depending on temperature and humidity.

 

I like 1/2" wallboard because it is not so heavy in the bigger pieces. I tape all the edges, because any crumbs of gypsum floating around the studio will invariably show up as pop-outs. After I have used a board, I stand it on edge to dry.

 

I have given up on using newspaper with slabs. It expands and wrinkles when wet, or tears. I have been using cloth to keep my slabs from sticking to things, and to absorb moisture evenly from the bottom of the piece. Old canvas or twill or denim shirts are great, cut up into the sizes you need. Even chamois-cloth. So I roll a slab, cover one side with cloth, put a piece of wallboard on top, and flip it onto the wallboard. Then I cover the other side with cloth and another wallboard, and wait for it to set up to the right consistency for working. I put smaller pieces of cloth between the slab and my mold, and, the next day, another smaller piece between the piece and the wallboard when it gets turned upright. If you dry them by hanging them up, rather than in the dryer, they don't appreciably expand when they get damp.

 

As for bottoms of plates that hump, I learned a great tip in a workshop by William Carty. As clay dries and is fired, it shrinks to a fixed density. When you compress clay, you increase its density, so it shrinks less in drying and firing. So, if you rib one side of a slab when you put it into a press-mold, but not the other side, the top will be compressed more than the underside. The underside will shrink more than the ribbed side, and the bottom of the plate will hump. You think you can prevent the humping by weighting the slab as it dries, but the uneven compression will show up in the firing.

[Ginny C]

My cracks come on the edges or rims, not ever in the center, even though I always cover them with thin plastic and tuck it in around the sides.  This happens especially on dishes made from a slab with incised patterns, such as from doilies or string nets pushed into the clay (and removed) before the slab is draped over a mold. The rims are gently ruffled in and out.  Sometimes a crack appears as the piece is drying, and it is inevitably at a stress point where an incised line gets close to (or at) the edge.  

 

I may need to have my edges thicker! I do try to have the slab an even thickness, but it often ends up thinner at the edges once it's draped and shaped.

 

I have just now tried putting thinned wax resist on the edge of one dish I made today, but how far in should the wax go?  1/4 inch? 1 inch?  And would vaseline be better than the wax?

[Mark C.]

(slab is draped over a mold)

As the clay shrinks the mold does not and puts stress on the clay-hence cracks.

I prefer slump into molds- not over molds the clay shrinks away from the mold and stress cracks are less.

as far as waxing the edge-if you are trying to slow down the dry more is better.

Mark

[oldlady]

ginny c.  how about trying something as an experiment.  you will only lose one piece if it doesn't work and i won't bother you again.  roll out a slab about 1/4 inch thick.   use a wallpaper smoother or a drywall tool to remove all the canvas marks and make the surface very smooth.  rub the slab hard with either of those tools holding the tool down as flat as you can, just don't catch your fingers in it.  ON BOTH SIDES!!  (compression)

 

 then put your doily down and roll it into the clay until the threads are sunk into the clay and the slab is level across the surface.  this is hard to explain in words.  if you were to now run the drywall tool across the slab while the doily is still on it you would not snag the threads because they are sunk into the clay. you would not scrape any clay you would just pass over it. use a needle to cut around the shape of the doily leaving what margin appeals to you. to prevent any cracks where the doily has an abrupt change of direction, press a finger or tool firmly into the edge of the clay forcing it to compress toward the center. ( this is the technical  part.)  _______ Do not miss post #35 below.

 

with the doily still in the clay, place the slab INSIDE a bowl, dish, hole in plaster or wood or whatever will give it the final shape.  if you want ripples in the edges, simply  lift sections evenly and stuff paper towels or something like that under the lifted sections. treat the whole thing so you will be happy with the ripples once it dries. leave the edges alone until later. (the artistic part)

 

using both hands, slowly pull the doily out of the clay and gently smooth the surface that remains.  you must take care not to leave sharp edges where the threads come upward out of the clay.  if you find any, just place a thin cotton fabric like a handkerchief over the surface and rub your thumb gently to flatten anything that sticks up.   ( if you don't, there will be cuts on your hand once you glaze it and run a finger across the surface.)

 

here is the hard part. DO NOT COVER ANY PART OF IT WITH PLASTIC, CLOTH, WAX, OR ANYTHING.  just let it dry.  if you have rolled your slab evenly, it should dry without cracking.  once it dries, use a damp sponge to round over the edges top and bottom.  do not use too much water, especially where you compressed the edges toward the center.

 

i can hear a lot of protests from people who make half inch slabs and think thinner is crazy, but it works.  yes, the thickness where the doily threads were is now less than a 1/4 inch.  as long as the doily is not made of rope it should be just fine. and i assume you know enough to line your mold with a resist. try it you might even like it.

[Ginny C]

Wow. Thanks, Old Lady! I will try this...and might try the technique of cutting around the patterned area after the material is impressed and still in place.   To use the styrofoam hemisphere as a drape mold (when I really want the fully round bottom, to add a thrown flared pedestal to), I will still need to remove the netting or doily before flipping the slab over and placing if on the mold...but I will add your method to my repertoire!  And cutting outside the impressed lines will probably limit any cracks there.

 

And Mark, the flared edge where the crack occurred was several inches beyond the drape mold, so I don't think the shrinkage caused it, other than the uneven drying.  I was pleasantly surprised that the clay lifted easily off the styrofoam mold when leather hard. No resist added, either!

 

What a great service this forum is—thank you all.

[oldlady]

be sure to compress any areas that are where a V type cut are.  the bottom of the V is where cracks begin.  even if it is not a sharp V, the clay needs compression right there.  use something round and firmly drive it into the area where the V is the sharpest.  very hard to say in words.  

 

if you want a big, round bowl, go buy one at your local thrift store and use the interior of it.  WD-40, cooking spray or cloth make a good separator so you can get your clay out once it dries enough to handle. 

[Chilly]

be sure to compress any areas that are where a V type cut are.  the bottom of the V is where cracks begin.  even if it is not a sharp V, the clay needs compression right there.  use something round and firmly drive it into the area where the V is the sharpest.  very hard to say in words.  

 

 

My Engineer other-half calls this "crack propagation".  I have a tiny brass tube I use to cut inside corners, and then use a knife/needle tool/whatever to cut away from the tiny circle.  I used to get cracking from inside corners, now - ta-dah - no cracking.

[oldlady]

thank you chilly, i forgot that i do that too.  and once the circle is cut with a copper tube,  i press the tube firmly into the curve.  you said what i wanted to but could not.  thanks again!

 

copper plumbing parts are really cheap and various sizes are available for less than a dollar each.  look for slip couplings to use as cutters.