Tuesday, February 13, 2018

Tuesday, August 15, 2017

Crack Spackle

HINT OF THE WEEK: Super-Strong Slip For Attaching Wet To Dry Clay Pieces! Patching Cracks! Fixing Broken Greenware! And Even Joining Broken Bisqued Pieces! From the FlyeSchool.com


Paper Clay Slip or Magic Mud: For more extreme issues with patching or joining broken-off bone dry clay pieces or even bisque-fired pieces, or for just making sure those joins between leather hard slabs won't crack, a slip made of paper, clay, and magic water, or vinegar (à la Martha Grover) or various other mixtures might be just the thing. The paper fibers added to the mix help hold things together against drying stress, make it easy to re-wet and also fast-drying. THIS STUFF STINKS if it's left around long enough for the paper pulp to rot - it's best mixed up as needed.

Again using a recipe from Lana Wilson:
1/4 to 1/3 toilet paper by volume
2/3 to 3/4 broken up bone dry clay by volume

Put the clay and paper in a bucket and add magic water until the liquid level is an inch or so above the paper and clay. Let the bucket sit overnight, then drain off excess water and mix up with an immersion blender or regular blender. Use it at slip consistency for joining leather hard pieces, or dry it out to a putty for patching up cracks.


HINT OF THE WEEK: How to Re-Glaze a Piece

  copyright 2000, Cindi Anderson,  www.bigceramicstore.com


First, note that this process is never predictable. In most cases you can make a new piece in less time than you can spend re-glazing it, with much more predictable results. But sometimes there is that piece you can't part with and really want to re-glaze. Here are some things you can try to increase your success rate. The goal, of course, is to get the new glaze to stick to the old glaze.

·         Spray the piece with spray starch, let dry, then reglaze.
·         Spray the piece with sticky hairspray (usually the cheapest you can find), dry, reglaze.
·         Heat the piece first, with a heat gun, torch, in the oven or a kiln.
·         Brush white (Elmer's) glue on, let dry, reglaze.
·         Microwave the piece for 30 seconds. (Some potters say this makes a huge difference, and the piece doesn't need to actually get or stay hot)
·         Add some suspension agent to the glaze (CMC gum or Bentonite.)
·         Add some detergent / shampoo to the glaze (baby shampoo is good because it doesn't foam)
·         To improve your odds further, wash the pot first with ammonia or detergent, wearing rubber gloves, and don't touch it. The oils from your fingers can prevent glaze from sticking.
And... Don't use too much of anything. If you get the coating too thick, you may prevent adhesion instead of encouraging it.

Monday, May 22, 2017

Hint of the Week

How to Dry a Platter Without Cracks

 by Mea Rhee, Good Elephant Pottery, 05/30/2010

Here's what works and what doesn't, after months of trial and error. I'm talking about wheel-thrown serving platters, between 16 and 20 inches across when freshly thrown. Until this year, I rarely threw platters this large. They cracked while drying on a regular basis, I'd say 1 out of every 4 developed a crack in the middle of the floor. I considered the cracks to be random occurrences, because I had not bothered to analyze the problem. This year, as part of my wholesale orders, I needed to produce roughly a dozen big platters. When two of the early ones cracked, I started looking for answers. And here's what I figured out.
First and foremost, a large platter requires good throwing and trimming. It must be evenly thick throughout, and well-compressed as it is thrown. A thin area will crack, and a thick area will crack, because these cause uneven drying and shrinking, which the clay cannot tolerate. This factor requires experience and good technique, which every potter possesses in different amounts. But here are four factors that everyone can control right now:

1. Dry the platter on a melamine board. Melamine has a non-absorbent hard plastic surface, with a slightly grainy texture, that does not bond with leather-hard clay, therefore the platter is free to shrink as it dries. The other choices in my studio are wood and drywall, which are useful for other pots but not for large platters. A wood board warps when it becomes damp. A drywall board doesn't warp, [but its paper surface becomes spongy when wet and the platter may stick].

2. Dry the platter on its rim. All pots dry from top to bottom, and a rim dries much faster than a floor because its surfaces are more exposed. So drying a platter upside-down evens out the drying process. When dried right-side-up, the rim will harden and shrink much faster than the floor. When the floor tries to shrink later, the hardened rim does not allow it, and the floor splits open.

3. When the platter is upside-down, support the floor. Before I flip a platter over for trimming, I stack a combination of studio sponges, upholstery foam, and 1/4 inch thick scrubber pads, in the middle of the platter flush with the height of the rim. So when the platter is upside-down, the floor is supported from underneath. Without the support, sometimes the floor of the platter would sink downward while trimming, and these platters were guaranteed to crack later. My (unsubstantiated) explanation is that the flexing caused micro-cracks in the leather-hard clay, which grew into visible cracks later. I leave the supports under the platter for its first few days of drying. As soon as the platter is stiff enough to be picked up, I remove the supports so there is nothing to prevent the platter from shrinking.

4. Cover the drying platter with fabric. My basement studio is very drafty, and uneven drying is a constant battle. But a sheet of fabric is all it takes to slow down and even out the drying process for a platter. Any lightweight fabric works, like an old t-shirt or bedsheet. A sheet of plastic also works, but it slows down the process too much. Using fabric, the platter is ready to fire in 8-9 days. Using plastic, the platter takes 3-4 weeks to dry, unacceptable for a wholesale schedule.

All of these techniques can be summed up thusly: even out the drying process, allow the pot to shrink, and don't allow the pot to flex. I am happy to report that after incorporating all four of these factors in my platter-making process, I have not lost a single platter!