I don't know what happened with this particular piece, but the results are weird for sure. I've used Pearl Ex, and CR Loo's micas for glass many times and never had a problem before.
I haven't finished the piece with the problem so I will do some experiments and see what happens. I have scraps of the glass too so will experiment with them as well.
Ron
Ron
I'm going to take a guess and say that maybe in the piece that got the pitting, the mica stuck better than usual. This would cause it to act as a better sandblast resist, which would result in an uneven blasted surface. Since I'm not looking at it, I might be way off, but it did strike me as an explanation of why the result could be different.
Avery
I wish I had a tape recording of the conversation I had with Bill Helwig about Rainbow Lusters. He basically told me to go to Michaels and buy a different product. As I recall the product wasn't exactly pearlex, but a fabric paint that contained the micas and is made by the same manufacturer as Pearlex. I believe that he told me that Thompson was just reselling the Rainbow Luster product and that I could save money with the other stuff. I think that I extrapolated that plain pearlex mixed with a medium would do the trick.
There may be some truth to what you say Bert. There is a difference in the way micas blast compared to bare glass. When I do a piece, I stencil the general area I want color and airbrush on the powder and fire it. After that, I mask with clear resist and cut a design. With something like a solid shape, a square or round, the color spot might be 1/8 inch bigger than the finished size and I have seen a layered look to the blasted surface. Almost like the surface was stage blasted. The micas must be resisting the blasting more than the glass.
As for the powders, Carefree (Lustra Cotes Inc) has 3 patents listed, but they all pertain to the application of the powder and not the powder itself. I haven't found anything on Jacquard (Pearl Ex). From reading about mica powders the process to make them sounds very similar to what it takes to make dichroic glass, not something everyone has the equipment to do.
This isn't a mica specific problem. While I have a number of pieces that have the bubbles like you mention under Aztec gold mica, I also have a number of pieces of irid that developed a powdery "look" to them after 1 firing against the kiln shelf. What I found was that I could push a scribe right through the powdery areas and into the porous glass beneath the coating... The glass was so soft, I could carve into it with a knife. After sandblasting off the irid, it was clear that the glass under the irid had become spongey... but only under the areas of irid that had that powdery look to them.
Now it becomes a chicken and egg question... did the glass develop the microbubbles which affected the coating, or did the coating react with the glass and create the bubbles.
Tony
The tightrope between being strange and being creative is too narrow to walk without occasionally landing on both sides..." Scott Berkun
I pieced the scraps together for the bowl with the bubbles under the Pearl Ex Aztec gold. Since its been about two months since I started this piece my memory was growing dim on what I did.
This piece was made from cutoffs of black and SILVER IRID black and has had a history of problems. This poor thing has been fired 4 times and along the way I removed the irid coating and flipped the piece over and refired, looking for a pit free surface. About this point I broke it by heating too fast, and the story goes on and on.
There is good indication that the micas were applied to the side that originally had the silver irid coating which may have caused the bubble troubles.
This stupid thing still isn't finished and about the only thing I can think of doing is keep on firing till its right. While I fire it yet another time with micas on the back side I'll put a piece of silver irid in the kiln with irid removed and add some gold mica to see what happens.
Bonnie Rubinstein wrote:Thanks for the tips.. once again, the gold leaf burned up when I sandwiched it between 2 layers ( is going to 1450 too high?) .. oh well.. may try the gold foil.
However, I did have success with the mica powder, finally,- applied it very thickly to the underside of clear, then placed on top of black.. it works, but it is thick and mat... I am looking for a shinier gold, sheer- almost 'mystical' appearance of the gold..
Alice, if you have a business phone # and tax ID #, I believe you can order from Ed Hoy.
Bert, you mentioned pulling the glass with the gold foil sandwiched. At what temp did you do this? I was curious as there was much discussion regarding it burning out or was that just leaf. Thanks Linda
Linda Hassur wrote:Bert, you mentioned pulling the glass with the gold foil sandwiched. At what temp did you do this? I was curious as there was much discussion regarding it burning out or was that just leaf. Thanks Linda
Linda
I was referring to the stretch from a slump. This will happen before the burnout temp of foil. It comes out lacy.
Ron Coleman wrote:Update on my mica bubble problem.
This stupid thing still isn't finished and about the only thing I can think of doing is keep on firing till its right. While I fire it yet another time with micas on the back side I'll put a piece of silver irid in the kiln with irid removed and add some gold mica to see what happens.
Ron
Please keep us updated on your tests. I've stopped using irid on the shelf side after ruining 3 pieces. I thought it was just a particular sheet of glass that maybe wasn't up to standard, but it recently happened again, this time with clear rainbow irid. Wrecked what would have been a lovely piece and one that had a lot of expensive glass in it (urobium pink, neo-lavender, goldpink). I sandblasted off the mess (but you could still sort of see some of the deeper pits) but it didn't have the effect I wanted without the irid. It goes in the middle or on top now.
What do you think would happen if the glass was taken to say, 1550 to 1600 degrees, and the glass manipulated like you do when combing? Do you think the gold would burn out? I'd try it, but don't want to waste a piece of gold foil. Thanks Linda
When I made gold decal sheets in the past and applied it to float that was stretched during the slump, the gold would sometimes tear. Combing could have the same effect I would expect but I have not tried it. Kevin
