Mica disaster what did I do wrong?

[Flowers]

Hello I have had a fun time experimenting with some Bullseye mica.  I have not used it before and I don't know where I went wrong.  I made a Stencil design using fine coloured Bullseye powders sprinkled on 3mm Tekta and then tack fused this.  It cane out quite nicely but I decided to have a go with Perfect Pens and draw around the pattern and then sprinkled mica on for emphasis brushing off the remainder.  Then I became stuck should it go back in the kiln on a full or tack fuse.  Should it be capped etc etc
So I put the piece back in the kiln capped with another 3mm of Tekta and put on a full fuse.
On opening the kiln I can see that all the mica has disappeared!!!! I also have bubbles in the piece.
I do not know what I did wrong and would love some help and advice. 
At what point can mica be incorporated and should it be tack fused or full fused, capped or not capped?
Thank you so much for any help.

[Zeldazog]

Hi

I've only used mica in a fairly minimal capacity, but I don't cap it, I use it top surface only.  When it comes out, usually some will rub or brush off, but then left with a subtle sheen.  As far as I am aware, only a particle thickness of mica will stick to the glass, the rest doesn't stick - so you cannot add more mica on top of mica to make it thicker or shinier. 

If ever I have got mica underneath and inbetween anything that was supposed to be fused to the base glass, the top piece has come away (frit or caps for wire loops)

I'll guess that the bubbles have formed where a) the mica as prevented the glass from fusing together due to it's own properties and b) offgassing of the perfect pens, nowhere for the product to escape.

I don't know the optical properties of mica and what makes it have such a sheen, but I am guessing that by capping it, you negate those reflective properties.

Why not make some test tiles - all you need is a one inch square of whatever glass you're wanting to use, and try each of the possible variants, you will learn so much this way.  Better to spend a quid on electricity firing a kiln with only test pieces in than spoil something that you've made.

I think some people have mixed mica with a medium of some sort, spread it onto some sort of carrier paper, and then cut shapes out with it - may be use the search function of the forum and see if there are any other posts about mica.

[Dietmar]

Glass can dissolve other silicates at high temperatures. Mica is an alumosilicate (...). Due to the fact mica breakes into very fine layers the process of dissolving is not uncommon.  Some minerals let go gasses while dissolving in glass and mica might let go water while heated.

Was the mica in coarse flakes or a fine powder? Powders will make thinner layers and dissolve faster. If the mica does not dissolve it also does not hold the base and the capping layer togeather. It acts like a separator and might create undercuts or seeds for cracks between the layers.

Bubbles under a capping layer of clear glass are always a problem if there are trapping structures underneath. Each elevation (frit, stringer, ...) will trap air because the edges of a capping layer sink faster to the base than the supported parts.



Some ideas for the second try:
- Use 6mm tectra and stay with surface decoration if you want to fire for full fuse anyways.
- After adding the frit and drawing heat for the frit to melt flat.
- Use the mica with a water based fusing glue as a painting medium to spread it on the glass surface.
- Never mix mica and glass powder (enamel, ...) because it will create a permanent rough surface.

[Flowers]

Hello thank you both sooo much for the advice and information.  The mica was in powder form.   I am going to try again as suggested with little squares and see what happens capped and uncapped a nd try mixing with a glue or some such as well.  I hope to have better success with this medium in the future.  Thank you both for helping me out :-)