Thursday, June 22, 2006

Trust Yourself

No coffee yet--I have got to start remembering to set it up at night before I go to bed. No music either--Dave and Jessie both still slumber peacefully. I started my morning with the peaceful activity of fiddling with the pond fountain to make it spit more muddy water (I don't think it is ever going to clear) and feeding the fish. Just knowing that they are all still alive is very comforting.

At right is the result of yesterday's combing. The colors are Egyptian blue and French vanilla (blue? it looks black! well, now it is black...). I am reminded of a valuable lesson that I had thought long ago learned: do not take the easy way out and follow someone else's directions over your own instincts. For whatever reason, most of the glass community likes to kilnform their glass at very high temps. I don't. I never fuse at the common 1500 degrees--1465 in one kiln and 1440 in the other for full fuse.

Yesterday when I decided to comb for the first time in many, many years, I looked in my kilnforming library for a recommended schedule instead of going back through my firing logs. Logs for the past few years are on the computer and, until my time got consumed with blogging, writing and gallery popularity, I was slowly working my way back through the paper logs and getting them online for easier searching. The library was more easily searched.

The first schedule I found called for a fuse temp of 1700 degrees--100 degrees higher than I had set the kiln to go. I went with my instincts and programmed the kiln for a soak at 1600, at which point I would turn off the kiln, open it, comb, close and restart. When it was at 1535 degrees I chickened out (if it is in print, it must be true) and set it for 1700. Mistake. I might still have lost the firing, but the problems with it would have been my own.

Why not go to 1700 degrees? Because it is overkill. Yes, at that temp you can rake several passes before the glass cools too much and you have to re-heat it, but the rake has less drag and so moves less glass on either side of the contact point resulting in a smaller pattern. Colors in glass made for kilnforming at lower temperatures can also change--the blue I used went to black and that might be from exposure to the French vanilla, or it might be the high temp. When I do melts from a flower pot my reds always go to muddy brown at that temp. At that high temp you also run a greater risk of air bubbles. An finally, kilnwash is not as effective and you almost always have to scrape, soak and use acid products (or sandblast) to get it off.

So I am going to redo this piece, and this time I will start at 1600 degrees. If that is not high enough, I will work my way incrementally up to find the lowest temp I can successfully rake at, and I will verify my belief that I will be able to do it with fewer bubbles and truer colors. I have to decide whether I also want to make wider stripes and use all transparent colors too. Maybe I'll do two sample pieces simultaneously to decide.

This would be a wonderfully fun puzzle if I were not under deadline!

4 comments:

Barbara Muth said...

egyptian blue reacts with French Vanilla.

if you want a list of reactives, let me know, when I get back in town I'll forward you my database. Test any colors before you hifire them, there are a lot of reactives.

Barbara

Brenda Griffith said...

I actually picked the Egyptian blue because it is reactive with French vanilla. However I thought I would get what I usually get which is a thin line of reaction--dark brown--where the colors touch. I was not expecting to lose all of the blue. That, I think, is more likely to be a product of the heat than strictly reaction--or maybe a better way to put it is increased reaction because of increased heat. Add that to the extreme opacity of the piece and I am going to be better off using at least one transparent in it (I am thinking of turquoise).

Thank you for the offer of the list, but I have a fuse strip of French vanilla with all the other opals which I did when I first got it and started playing with the reaction. Though I don't have anything for it with the cathedrals--that I would love to have (assuming there is a reaction, I would guess there is).

Bill Paley said...

Egyptians haven't gotten along with French since they fought over the Suez Canal. No wonder it turned black; too much history.

Barbara Muth said...

transparent turquoise reacts with the vanilla too. If you had wider strips of blue and vanilla, the problem probably wouldn't have been so pronounced. And I agree, the high heat appears to make it more pronounced. Good luck on the next try!!

Barbara