Super Spray A Reaction, Shadows, Polishing

[Franzeska]

I fused Spectrum stacked squares and I was pleased with the effect. The finished thickness of each piece is about 5/16". The two items are 7.5 x 7.5 and 6 x 9 inches.The edges needed some smoothing because of contact with fiber paper lining the dams. I used a grinder, cleaned the ground edges as best as I could, and opted to fire polish to round the ground edges. I thought Super Spray A would help things along and decided to brush it on the top as well. The shelf had been fired only once since being scraped and kilnwashed. I used Thinfire this time around. I'm pretty sure I did not hold it long enough at the process temperature (2 minutes @ 1375), but I think there was a reaction to something in the Super Spray because the glass developed brown areas, basically on the yellow and green glass. The bottom of the piece also now has shadows of some of the design squares. I have no idea what was in the Super Spray to cause the brown reaction. I've used this same bottle before with no problem. Could the little mixing balls have deteriorated over the last 2 years and leached some metal into the liquid? Or would I not have had the problem if I had held it for 10 minutes?

Problem #1 Salvage the pieces by shining them up. I have never done serious coldworking with hand pads because I used to live near a studio that had all the equipment (lap grinder, sandblaster, etc.) Now that I've moved, I don't have access to equipment. I succeeded in removing the brown stuff on top, but I think I pressed too hard with the roughest grit pad, and I've got lots of scratches. I used all the grits up to 3000, changing the water after each grit. I don't want to use the pads further for fear I will mess it up even more. Also, my carpal tunnel issue can't take much more action. I'd like to re-firepolish, but I thought maybe I should sift clear powder or fine frit on the top to help heal the scratches. Is that necessary? Will that solve problem #1? Maybe there is a better solution, like driving 250 miles to use a sandblaster for 60 seconds...


Problem #2 Make sure the shelf is not contaminated. Brad's book says to fire a shelf to 1650 to burn off residue of whatever may have caused a reaction. Do you think that will work here? I can't find the page in the book to check the length of the hold...

I'm including a picture of the hand pads, in case anyone has any comments on them. They're supposed to be diamond pads, but who knows???

Thank you for reading all of this. I hope you have suggestions on how to solve my problems.

[Brad Walker]

I probably wouldn't have used a devitrification spray here, but that's water under the bridge. (Did you use Super Spray or Spray A -- two different products?)

The brown areas look like a reaction with silver to me, but there's no silver in Super Spray or Spray A and the mixing balls wouldn't be made of silver either. Was there anything else with silver in the kiln? Or could the brush you used have been contaminated?

You're right that a sandblaster is the best way to remove stains. Diamond hand pads are a poor second choice, but if you can get the stains off with them you'll only need to go down to around 400 grit -- grits finer than that won't help much and anything finer than 800 is basically worthless on glass. (A basic glass set is 60, 100, 200, and 400 or something like that.) You can put a layer of clear powder on top before refiring, but make the layer very thin (one or two grains thick) and all over the top of the piece, not just in a few areas. You'll need to go higher than 1350F to get it to shine up again, probably closer to 1450.

(If you have the ability to set up a loose silicon carbide grit and plate glass coldworking area, that's much better than diamond hand pads for flat surfaces. And cheaper.)

If the shelf was contaminated, the stains would almost always be on the bottom of the piece, not the top.

Next time you clean up the edges with a grinder, just do a final pass with a fine grinding head on the grinder (instead of the standard grinding head). That removes the grit from where you ground with the standard head and you won't need any devit spray or anything else. If you don't have a fine grinding head use your 400 grit diamond hand pad on the edges.

[Franzeska]

Brad- Thank you for your comments. I really appreciate them.

I removed the stains. I didn't think the brush I used with the Super Spray A was contaminated, but I didn't give my husband the 3rd degree to see if he borrowed it. There were some dichro pieces in the load. Could that have caused the problem?

I'm seeking a sandblaster in the area.

Again-

Thank you!!!!!!!!!!!!!!

Franzeska

[Brad Walker]

There were some dichro pieces in the load. Could that have caused the problem?

I doubt very much that dichro caused the problem. More likely something else.

[Marian]

I have taken pieces to be sandblasted to an automotive machine shop. They use big blasters to clean parts and may be happy to sandblast your piece inexpensively. They don't do delicate decals, but an overall blast is not out of the question.

[Dick]

after you get it back make sure and clean very well with alcohol as they will probably have minute bits of metal from all the metal they blast