Expensive Lessons

[Larry Lunsford]

A friend recently commissioned me to make a pair of glass panels to go around a couple spitters on his pond.

The project seemed simple enough. They did want A LOT of dichroic in the pieces.

The bottom layer is black with gold irid. Top layer is clear. Design in dichroic is in middle.

In my first attempt (top left) I anticipated bubbles would be a problem so I cut top clear into 4 pieces. Didn't have bubbles, but joints drew up dichroic and irid to surface and left ugly scars.

Second attempt (top right): left top in a single piece. Came out pretty good with only minor bubbles. Pieces did move around a bit from where they were when I started kiln (used GlasTac to keep parts in place). Suspect that top layer of clear trapped enough gas to cause moving around.

Third attempt (bottom left): more problems with bubbles that drew dichroic / irid to surface. Used supposedly same color dichro from different sources - final result showed major difference in appearance. Also had problem with pieces moving around.

Fourth attempt (bottom right): First firing tacked fused dichro parts to clear (eliminated problem of trapping gas and parts wiggling around). Second firing fused black / gold irid onto clear with dichro (clear still on bottom). Some bubbles could be seen through black. Third firing: sand blasted clear and did fire polish with clear side up. Going from one firing to three eliminated problems of trapping gas from GlasTac and moved bubble crap to back where it was not a problem.

I did some test pieces that were much smaller (for color testing). Didn't discover problems until I did piece in full size (they're 13 inches across).

I've learned a lot from reading this bulletin board. Hopefully my experience will save some of you a bit of grief and expense.

Larry

[DonMcClennen]

I doubt GlasTac (gas?) caused any of your problems. ..I've been using that stuff for over 20yrs. it is gone by the time your firing reaches 300F.

[Morganica]

Possible issues:
1) If you still need the GlasTac when the piece is sitting flat in its final spot in the kiln, you're probably going to get movement as soon as the Glastac burns off--the pieces will still be hard, slippery and subject to gravity.
2) Check your schedule. The faster the glass softens on the way up, the more likely you are to have movement.
3) Black will soften and flow faster than any other glass (unless you've got a specially-hardened glass like BE Stiff Black), so if it's flowing while surrounding a glass that is still stiff, you're more likely to get movement.

[Valerie Adams]

I would've fired these pieces with the dichro on the black face down on the shelf. Then, in a second firing, cap with clear.

[Nina Falk]

Irid fired face down onto thinfire can leave a cloud on the glass...don't know if it happens with dichro.

[JestersBaubles]

Irid fired face down onto thinfire can leave a cloud on the glass...don't know if it happens with dichro.

Dichro face down is just fine. Leaves a nice texture.


Dana W.

[Nina Falk]

it "can" leave a cloudy residue...may not happen every time. if you're lucky, it won't happen often.

[JestersBaubles]

it "can" leave a cloudy residue...may not happen every time. if you're lucky, it won't happen often.

It can leave a cloudy residue on irid, but I have not had it affect dichro.

Dana W.

[Nina Falk]

that's good to hear. thanks for sharing your experience.

[Jerrwel]

The bottom layer is black with gold irid. Top layer is clear. Design in dichroic is in middle.

Not really certain..is this a 2-layer design with significant decoration elements or a 3 layer design >1/4 inch in depth? If so there will be movement as the glass will spread if not dammed.