Sandblasting Question

[smallbitz]

I have just sandblasted two pieces that have pattern bar inclusions, but the basic design is mostly clear glass. The pattern bars picked up kiln wash and needed to be blasted off, so I just sandblasted the entire bottom of the pieces. After some cold work, I fired again to fire polish (around 1300) and the bottom of each piece was still matte. Looks nice, but not what I intended for the pieces. I suppose this has happened before, but I didn't notice it until the clear glass. Do I need to flip and fire, then fire AGAIN to get a gloss back on the top? Then slump...

Thanks.

[DonMcClennen]

1300 is too low for fire polish.

[smallbitz]

Sorry, I meant 1400. They are flat pieces. Tops and sides look great, but bottoms are still quite matte.

[Jerrwel]

I have just sandblasted two pieces that have pattern bar inclusions, but the basic design is mostly clear glass. The pattern bars picked up kiln wash and needed to be blasted off, so I just sandblasted the entire bottom of the pieces. After some cold work, I fired again to fire polish (around 1300) and the bottom of each piece was still matte. Looks nice, but not what I intended for the pieces. I suppose this has happened before, but I didn't notice it until the clear glass. Do I need to flip and fire, then fire AGAIN to get a gloss back on the top? Then slump...

Thanks.

Is COE shift a concern in this situation? You already have had at least 3 firings with pattern bar elements and are thinking of maybe 3 more firings? If the investment in these pieces is low enough you might want to experiment to see what happens as you progress with just one of the pieces. Alternatively, I'd think about slumping 'as is' if finish is acceptable even though not what you planned. Maybe consider using a low-firing over glaze such as Fuse Master's 'Bending Glaze' which according to Paul Tarlow matures at 1100F when slumping.

[smallbitz]

Actually, they are test pieces. One of them I thought was a lost cause that had been sitting in my studio for a couple years. Finally invested in my own sandblaster 6 months ago and thought I'd try to salvage it...I may just go with the matte finish on the bottom. It does look nice!

Thanks.

[Jerrwel]

Actually, they are test pieces. One of them I thought was a lost cause that had been sitting in my studio for a couple years. Finally invested in my own sandblaster 6 months ago and thought I'd try to salvage it...I may just go with the matte finish on the bottom. It does look nice!

Thanks.

If just test pieces, why not do the higher fire to get the gloss finish you want and then slump to see how they do? If they are tests, test the heck out them!

[Stephen Richard]

" Do I need to flip and fire, then fire AGAIN to get a gloss back on the top? Then slump..."
Yes

[charlie]

it's fusing. you can't get all sides to be shiny. whatever is against a mold will always be matte to some degree. a blasted surface will be even more matte than a non-blasted surface, if it's against a shelf.