Lowest temperature for mica

[lmartine]

Hi,

I often see a 'do not exceed x degrees' if fusing mica powders, but I never came across a 'you need at least y degrees' for fusing them!

Would mica stick to a pre-fused blank if applied and then heated to, say, slumping temperatures (e.g., 1150F-1175F)?

Lucie

[Bert Weiss]

What kind of glass? They behave differently. Slump temperature is not hot enough. To stick on it's own, the glass must be hot enough for the mica to sink in.

[Valerie Adams]

A general rule of thumb is that mica needs a full fuse temp to adhere to the glass. It'll act as a separator if you place it under your glass (against the shelf) and won't stick at all.

I've tried it with slumping, which doesn't work for me (I only slump at 1150°) but I've had some success at firepolishing temperatures, which are around 1325° in my kilns.

[Barry Kaiser]

There is no chemical bond between mica and glass. It is strictly a physical bond. The mica sinks into the glass surface (thanks to gravity) and is held in place. Softer glass, better adhesion.
There are other variables also. The larger the particle size of the mica, more it sinks in (weight of the particle). Another factor is the coloring agent. Blue and purple agents do not withstand heat as well as the metallics (and to some degree green).
Having said all that, the best way to determine your situation is to experiment, both with the glass you intend to use and the mica.
Oh, one other thing. There is no such thing as standard mica. We are experimenting with micas right now and I can assure you there are literally hundreds of micas in every color.
Will be doing a blog soon on the experiments.
Here is one run:

[Bert Weiss]

I work with micas on float glass, which is much stiffer. I mix it in with frits, clear or colored. The frits manage to stick it well.

[Vonon]

Nice samples Barry. Looking forward to your blog.

[Valerie Adams]

Hey Barry, are those samples pre- or post-firing?
They look great!

[KaCe]

I was told that one can reuse mica that hasn't stuck to the glass, but when it came out of the kiln the mica was transformed from a gold to a rust color. I didn't know if the color was okay with me, if the mica itself would be okay? (I'm testing how the mica powder responds when used without a medium to hold it onto the glass… just using it dry. I sprinkled it over leaves and rained it down onto glass. I covered it with a cap and left the cap off. I'm terrible at taking notes. So I'm bogging down trying to remember things. I wish I had a good method to keep notes.


KaCe

[Barry Kaiser]

The samples are post firing. Below are samples of micas after a second -full fuse-firing. Held color pretty well.
Secret is two-fold.
First, we have found a supplier for the blues, purples and greens who services uses other than cosmetics. They still have some problems, but survive far better than what we found previously. We will be integrating them into our micas for sale.
Second, we apply the micas onto screen printed (and still wet) Kaiser Glass Paints of colors similar to the mica. We use blue base for blue, purple and sometimes green.

Still have problems with capped micas, but less so than in the past.