Happy Hallowe’en! & other (technical) topics

Working on a few projects at once, as usual. Keeps it interesting…

I have been working with bronze clay over the last few weeks. My first experiences were with domes that fired to about 1.5″ but I had some problems with uneven shrinkage so had to cut them to a smaller diameter. Warping is always a strong possibility, but uneven shrinkage is when the edges of your shape pull in; a circle is no longer a circle, in my case. I have been doing some research which has helped me consider the issues.

The following can effect shrinkage:
1) thickness–thinner pieces not only warp easily but if pieces have uneven
thicknesses, edge to center shrinkage can be affected, leading to #2
2) added decorations–I found that waiting for the dome to dry first, then
adding decorations later kept the dome from irregular shrinkage. Three other
domes I made in which decorations were added to the wet dome ALL suffered
shape deformations
3) with bronze, air quality can be important. Mardel Reins at Cool Tools cautions to keep air flow at a minimum, and humid air at a maximum. Uneven temperatures and pockets of dry/humid air will affect bronze clay more than silver clay. I have had very few problems of this nature will silver clay.

As for warping with bronze clay, it will likely happen no matter what you do. But fired bronze is easy to bend back into shape. One important point, though: after firing, it’s important to anneal the bronze because one dome I began hammering right out of the kiln developed cracks. Annealing prevents this.

The next photo shows a project in the works. The bronze discolors with firing; sometimes it’s a nice effect. This one is another disk with three cabochons on it for a pair of earrings. I made another pair like this earlier with three chrysoprase stones; the new ones will feature chrysoprase and…it’s a secret! These domes fired nicely and kept their shape despite the pre-cut holes.

I am very careful with arrangement of pieces in the stainless firing box, placing them at the back and sides, avoiding the front of the kiln if possible since it’s a front-loader. Always arrange the pieces in exactly the same way in the box–for example if firing a pair of earrings, place them in “mirror” positions along the same horizontal or vertical. There are other considerations such as gravity (fire domes in a “bowl” position). I use Mardel’s schedule for firing with can be found at www.cooltools.us.

So far I have been cutting holes for the fine silver bezel cups I am using, seen in the photo, but making my own bezels may be the next step. It isn’t easy to fire the proper sized hole so time’s spent filing them to the correct size. Then, bezel cups need more filing, or filling to make sure the stone sits at the right height. And another discovery: as an example, all 4mm stones do not fit 4mm bezels, and so on. I have had to stretch bezels because I don’t want to file a stone–but that’s an idea. It all adds up to more time and more cost to the customer.