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I was able to save this 17" X 19" piece by filling the crack with appropriate frit and firing very slowly. The piece is now whole but has what I think is devit. Dull haze over most of the surface and some of the elements of the design look as though they are no longer covered with clear frit. My first thought was to use Super Spray but that requires a high enough temperature to mature that I think I might be better off to add a layer of glass (frit or sheet) and fire to full fuse. Once again scared that I'll ruin it. It is one of 3 pieces (the other 2 are fine) and I just got them into a frame made by a local ironworker. I didn't think the surface was too bad 'till I got the complete piece on the wall where the lighting highlights the crappy surface of this one. What would you advise? This will be the 4th firing of a 1/2" piece. Me so afraid!!

Edit: I got very helpful advice in a PM and will go forward with the plan tomorrow.

It is very lovely. How about putting another Tree to cover the crack and more forground around the base of the tree and then cover the whole piece with clear frit and take NO more than 50 deg.F. per hour to bring up to 1230, hold for 30 minutes and then to top temp at about 200. deg F. per hour.
Leslie

Les, sent you an email.

Find someone with a sandblaster in your area and have them sandblast the entire surface, very evenly. Then fire slowly, just to a firepolish, and give it a slow cooldown. I like that better than sifting clear powder and refiring to a full, flat fuse--if you get the proportions of powder-to-glass wrong you can trap bubbles in the powder that create yet another haze.

The alternative to sandblasting, although it would take more work, is to get some wet-dry and do the same thing by hand. It won't take as long as you think, although it's a lot slower than sandblasting. Get a pack of wet-dry sandpaper from the hardware store and a stiffish sponge (one of those green scrubbies would work). Wrap the sponge with the sandpaper.

Then wet a piece of old towel/diaper/whatever soft, absorbent fabric you have lying around, put it flat on a waterproof surface (I use a jellyroll pan) and put the glass on top. Dip the sandpaper/sponge in a bit of water, press it against the surface, and start sanding. Use smooth, overlapping strokes, don't go so fast the sponge heats up, and don't put all your weight on the sponge (to avoid breaking the glass). Keep all the power at the surface of the glass.

You can also use a hard diamond pad for this, but it will take longer. The hard pad will wear off the top surfaces first, so to reach the entire surface you'll be removing a lot more material. (Fused glass is rarely perfectly flat). Another method is to get a thickish piece of plate glass, buy some loose 220 silicon carbide grit, and mix about two tablespoons with enough water to make a stiff paste. Drop it on the plate glass, lay your piece on it, face down, and move it in small circular patterns. That will completely flatten the surface of your piece and remove the devit on the way. Again, though, it's knocking off the raised areas first, and it can erase parts of a frit painting.

The sponge/sandpaper combination will follow the contours of the glass, and get you there quicker. It also lets you see what you're doing, so that you can control removal of material.

Grit size is going to depend on the degree of scum. 220 is about where I sandblast to. if the scum is extensive, and deep, I'd start with 100-grit and work my way up. For light scumming, though, start with 220.

Lovely piece, I hope that works for you.

It is out of the kiln and 7/9ths of it is a success. I combined suggestions and first used diamond hand pads to remove devit. Then added a few pulled tree-like things and added them on top of the crack area plus a little foreground frit. Covered it all with a layer of #2 clear frit and fired as advised. It came out very well except for the last area where I scrubbed devit. Didn't stay at it quite long enough and so have a small area in the upper left corner that looks like it has transparent-ish snowflakes under the surface. I put it back in the frame with the other two and will re-make it after I recover from knee replacement surgery which I am having tomorrow morning. Lesson learned!