I use an HVLP spray gun very similar to this one (mine have 1.4 mm tips, this one is 1.5mm)...
Some people tell me that you should really use a more expensive all stainless steel gun for glaze (or anything water based), but this super cheapie ($9.99 with a coupon, on sale often for $14.99 without) has worked really well for me so far. It does rust a little, but not anywhere important so far.
For spraying, I mix my glazes with between 80 and 100 grams of water per 100 grams of dry glaze. Shinos do really well with 80-90 grams, but I've had a little trouble with SCM and Watercolor Green gelling up and clogging the spray gun so I'm now using 100 grams of water for those. As somewhat of an aside, the standard recipe for Watercolor Green has 3% Bentonite and SCM has 2% Bentonite. I think those are too high for me and I'm definitely going to use a max of 1% next time I make batches of dry glaze.
The instructor for the class I have at the city art center showed me the basics of glaze spraying.
- The round knob behind the trigger is used to make the spray more or less round. I like mine to be pretty much a straight line. The other knobs are used to determine how much air and glaze ends up in the spray. The knob at the back is for glaze, the one at the bottom is for air.
- The front piece is adjustable. If it's horizontal (like the picture), the line of glaze will be vertical, and vice-versa.
- Use a turntable or banding wheel to rotate the pot while spraying
- Start spraying with the gun pointed to the left or right of the pot (or above or below) and move the spray onto the pot while spinning the pot.
- The basic "when it's done" rule is when the spray pattern on the pot stays wet (glistens) for 5-10 seconds after you stop spraying. "When it's done" is the real question, and I'll discuss further.
- Make sure to use some sort of glaze catcher until you know how much glaze you should put on. I use little clay "cookies" I roll out with a rolling pin. Most of my pots have a little ledge at the foot, which also helps to keep glaze from running off the pot.
- Many glazes will run off the pot if sprayed too thick. Others will blister or have other defects. Some glazes also look really bad if you put them on too thin. Shinos and many Tenmokus are good glazes for learing to spray since you can put them on really thick without running and they still look pretty good if you put them on a little too thin. I highly recommend Malcom's Shino and Penn State Shino.
With layered glazes, I had to pretty much figure everything out on my own. As you might have deduced from the info above, the most difficult thing about spraying is figuring out how thick the glaze should be. It takes practice, but it will probably only take you a couple test firings until you get it. Fortunately, SCM looks pretty good when it's on thin. The version without iron is kind of golden to tan colored (or kind of orange in reduction) and the version with iron is medium brown to fairly dark brown where thin. On the other hand, spraying SCM too thick can be fairly disastrous. It's likely to blister (or crater) and if you have other glazes sprayed over, it will probably run right off the pot. I spray the top and middle of the pots until the glaze stays a little shiny for about 3 seconds after I stop spraying. Near the bottoms of the pots, I stop spraying before I see any shine on the glaze. My pots are generally pretty thin walled (1/8" or less), so I try to have them completely dry before spraying. I pour the liner glaze at least 12 hours before I plan to spray.
If you're interested in this topic, hopefully the pictures of sprayed pots before and after firing will help. Feel free to leave a comment if you'd like more on this topic...
I enjoy yor blog and love your pots. I'm new to this and am having a terrible problem with spraying hanna's blue ash. I rarely get the dark blue rivulets that I'm looking for. When it's too heavy, I get solid bronze, and pots stuck to my new kiln shelves. When it's thin, I get a light tan. I'm firing to cone 6 with a Steven Hill scedule. I've tried it on the porcelain directly, but usually apply it over SCM. When you spray until the glaze looks wet for 3 seconds, aren't you getting craters in the wet glaze and drips at that point? Maybe I will have to wait till I can get to a workshop, but I really love the glaze and am determined to learn this spraying technique. Thank you for any insight.
ReplyDeleteI haven't actually used Hanna's Blue Ash. I have used Hanna's Fake Ash (the version with red and yellow iron oxide) with added cobalt to get teal or blue.
ReplyDeleteAre you using the ^6 version (with Frit 3195) or the ^10 version of Hanna's? I couldn't get the ^10 version to melt right lower than about ^8.
Assuming you're using the right version, you should apply directly to the clay for traditional ash glaze rivulet look. I generally want drips down into the other glaze so I spray over SCM and paint a ring around the lip of the pot to help it roll down. You could try painting or sponging on the ash glaze. It may make it easier to get a consistent coat thickness. I've done both.
Unfortunately, it's really hard to explain in words how the spraying is done. I definitely spray thinly, approx half the thickness of a dime for the SCM base layer. When I say looks wet for three seconds, I'm spinning the pot on a banding wheel quickly while spraying. I stop when there's a little gloss on the pot for three seconds (still spinning the banding wheel) after I stop spraying. The pot never looks drippy wet at all, just shiny/glossy rather than totally dry/matte.
To get rivulets in the glaze, I'd say you're probably shooting for about the thickness of a dime.
Do you have the Steven Hill video? It's definitely given me some new ideas to try which I'll do as soon as my pots are all dry enough and I get a day warm enough to spray.
http://ceramicartsdaily.org/bookstore/the-surface-techniques-of-steven-hill/
Hope this helps,
Anthony