Tag Archives: gyubera

My favorite studio tool…

….is without a doubt the Peter Pugger de-airing pugger/mixer. Until two years ago I did all of my clay and stone mixing in a large deep platter by hand, and it was killing my wrists.  Hearing all the wonderful things Peter Pugger had to say on their website, I took the plunge and decided to spend the money and save my hands. I figured if the thing worked half as well as it was supposed to, I would be ok.

Well, it is now about 2 years since I got it and it does everything it is reputed to do, and does it very well. My wrists are now pain free, and I have saved hundreds of hours of time processing and blending clay bodies.

Blending wet clay bodies usually takes about 15 minutes of mixing, but mostly I mix dry materials with water (sometimes blending into wet bodies), and this takes a while longer, usually around 30 minutes.

In my work, keeping the character of the wild clay is of utmost importance, and I’ve found that de-airing generally kills that character dead. However, the de-airing is necessary in getting the water to penetrate the dry materials more quickly, so that I don’t have to let the pugged clay sit for a month before using.

My solution to this is to let the clay mix, then I de-air it once completely, followed by re-mixing the batch for 5 – 10 minutes after reintroducing air. This gives me clay that is not as easy to throw, but which gives very nice trimmed texture.

Here are some pictures of some clay from the other day which I collected from the mountain behind my home. I added the dry/damp clumps of clay to the hopper (removing as many large rocks as I could find), then water, then mixed. I repeated these three steps until the hopper was full, then mixed for about 20 minutes, turned on the vacuum pump, and de-aired completely.

Next I went to lunch.  It was yummy. It was sunny on the deck and there was a cool breeze. The neighbors have a  great cherry tree in full bloom and the wind was blowing the petals off, and they were fluttering across the yard like giant pink snowflakes. I noticed as I saw some of them fall across the deck that the wisteria was budding out and even starting to show some purple. Nice. I imagine the wisteria will be in full bloom a few weeks early this year.

After coming back to the studio, I re-introduced air to the mixing chamber and mixed some more, then pugged it all out and made some pots. The whole process took about 2 hours. It takes even less time if you decide not to include lunch, but I recommend including it.

New Videos

I finally sat down and figured out how to use my video camera and software. For anyone who is interested, here are some videos I posted to youtube.

Karatsu Sake Cups

Sake Cup Trimming Part 1

Sake Cup Trimming Part 2

Karatsu Teabowls

Karatsu Teabowl Trimming

All of these pots were made with clay from the property, discovered right under where we built the kiln. It has a lot of iron, but still takes some heat, and won’t bloat at higher temps. Probably due in part to the fact that it is very open with a lot of sand and other even larger inclusions. Even vitrified, it still sweats because of the openness. With use, the sweating stops, as all the pores fill with minerals from the water and tea tannins, etc…

Gyubera, attempt #2

Who got the twisted James Taylor reference in the last post? Sorry about that, physical anthropology humor from a previous life.

Anyway, a friend came over yesterday and gave me a crash course in plaster casting. In one of his previous lives, he was a dental prosthetic technician and did casting in various materials for a living. My knowledge of plaster handling and casting jumped about tenfold in 4 hours.

We poured the mold similarly to before, with a couple of differences: he applied whipped cream consistency plaster to the backs of the originals, let it set, then turned them over and planted them in a freshly poured base, so the working side was face up. We cleaned up that surface in running water before it set completely, then applied separating agent and poured a different colored super hard type of plaster over the working surface of the originals. Then we leveled everything off with regular plaster. Mold finished.

Once completely set, I took the mold and soaked it in hot water for an hour to let it absorb as much water as possible, which helps the separating agent to work, and also keeps the plaster from absorbing liquid from the resin mix, which keeps the resin more fluid. Once the separating agent was applied to all surfaces, I put the mold together and tied it with old bicycle tire rubber, stood it up and poured in the resin. Then after letting the full mold sit for about 15 minutes, put it in a 50C bath for 30 minutes to cure the resin. This time I literally used the bath, and set the hot water temp for 55C. Much easier than a pot on the stove.

Once the curing was done, I let the mold cool, popped it open (which was easy with the proper separating agent) and out came two very nice gyubera. After trimming off the excess, and sanding them with a flap wheel and some 180 grit wet paper, they were finished. Victory! There were some small air bubbles but nothing like before, and the mold is in great condition for next time.

Hey baby, I’m your Homo Habilis…

Well, usually at least. This last couple of days was an exception. I started dabbling in some nifty new technology (to me). This involved casting some new tools, so when the old ones wear out I’ll have some ready to go. This tool is called a Gyubera, or cow’s tongue rib, that is sort of indispensable when making a lot of Karatsu forms.

The problem with them is that it is awfully hard to find them in the right shape for what you need. There are a lot of cheap ones on the market which are, well, cheap. The one thing they have going for them is that they have a lot of extra wood on them so you can do a lot of fine tuning with a rasp and sandpaper. The good ones are good, but cost a small fortune. I paid about $80 for my large one that I use for teabowls. Smaller one was about $50. Am I the only one that thinks that is ridiculous? Well, they were handmade one by one, by a barber. As strange as that sounds, there was this one barber that made really nice gyubera. He is now retired, and though someone took over his business, the new guy needs practice.

However, the big problem with all the aforementioned gyubera is that they are made of wood and prone to cracking and rot. It’s kind of a ‘heads I win, tails you lose’ situation. If you keep them damp, they rot. If you let them dry out, get wet, dry, wet, repeatedly, they crack. I found a partial solution to this by soaking them in Minwax wood hardener, and applying a layer of epoxy. But the epoxy bubbles up with time and they wood hardener wasn’t enough to prevent cracking over the long run, although it did extend the life of the tool considerably.

Not wanting to have to buy more, because of the cost and the fact that the new guy still needs practice. I thought I’d just make some myself, but it didn’t solve the wood material problems. So, these last couple of days I spent making plaster molds of the original gyubera, and using dental grade acrylic resin to cast new ones. I got the resin from a friend who used to be in the business. It is a funny pink color because it is supposed to look like gums. Aesthetically speaking, not my favorite for clay tools, but on the bright side it is unlikely I’ll ever get my tools confused with someone else’s tools.

After a couple of tries, I got a pretty good working two piece mold of two gyubera side by side. Got it ready for the resin pour and got the resin poured without too much fuss. Once it was poured and set for about 20 minutes, it was ready to heat cure in a 50C hot water bath for 25 minutes. Strangely, all of this went fairly smoothly. The problem came with trying to get that mold apart later. I tried and tried but it was not happening, and I ended up breaking the mold. Still, the casts were covered in plaster, because the liquid of the resin had penetrated through the release agent into the plaster. Oops, guess I should have used the special acrylic resin release agent instead of the casting slip release agent. Live and learn.

The cleaned up casts will make usable tools, but they are pocked with bubbles and other spaces where the resin didn’t flow properly. I’ll have to try again, improve the craftsmanship.