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can I slump a piece which is sandblasted on the mold side and have it get a matte finish or do I need to fire for the matte first then slump?

At normal slumping temperatures, a sandblasted surface will not firepolish whether it is facing the mold or not. Instead, you get a matte finish to the glass. To firepolish, you really need to bring the glass back up to fusing temperatures.

Tony

sorry- my question was not exactly what I have in mind, infact the matte finish is more what I desire. So if I understand you correctly Tony, it doesn't matter if the sandblast is down or up, right?

Not necessarily true. I sandblast my irids with 120 SiC and then slump at 1300 which has a beautiful firepolish edge to it.

Phil

Okay Phil... I said normal slumping temperatures... Jeeeesh!

Seriously, I know of people that firepolish at temperatures from 1275° and up, but the quality of the firepolish really depends on how smooth the surface is going in to the kiln. With that said, I haven't been happy with the firepolish on sandblasted glass until I'm up in the fusing range (1425° and above).

If you want the matte finish, slump at as low a temperature as you can (1150° to 1175° works for me) and hold for 15 minutes or so. I get the same finish up or down at those temps.

Tony

Depends on the glass too. I've tried the same firepolish on other colors and clear and they don't work as well. Black works great, but if my memory serves me correct, I believe it has the lowest melting temp so it would make sense that the black irid polishs nice where others do not.

Phil

I blasted the mold side of a piece of black BE and took it to 1250 for a slump. When I pulled the glass out of the mold, it still looked like it had just been sandblasted. Maybe a higher temp?

Greg,

Are you talking about getting a matte finish or a fire polish? The piece I showed earlier was slumped ar 1250° and had what I'll call a sealed matte finish as opposed to the powdery frost that you get with a freshly blasted surface. I've been gradually lowering my temperature and now I'm down to 1150° for 15 minutes with a nice, uniform, sealed, matte finish (up or down) and picking up no texture from the mold.

Tony

Tony,
I love that matte finish. This board is great. I still haven't accomplished anything good in my kin, but my head is spinning. So many ideas, so little technical talent. Sigh
Sandpiper

Keep trying Sandpiper... the good work will come of hard work and practice. It worked for me.

Tony

Tony,
Thank you for your support. Believe me, I'm trying daily. The husband is getting that glazed look in his eyes. The one that says I'm neglecting him, the teenager, the baby, the dog, the house. I found him gazing at the kiln the other day. I think he's trying to decide what its got that he doen't have!!!

I think I need to work smaller. I tend to jump in feet first. I actually fused a couple of piece with no bubbles But I don't like the edges, I don't like the look, etc. However, they were smaller pieces, less expensive and more manageable. What is my electric bill going to look like Let me guess, you fire three times. One to fuse, then fix the edges and fire polish, then slump. Am I right? My book is on thy way, and I've done everything just by the tutorial on this site and the suggestions of everyone. I think things will get clearer when I get to read the text!!!!!!!!!!! As soon as I get something that looks like something, I'll post a picture from the rookie. I'm sure you're all waiting with great anticipation!!!!

Thanks again,
Sandpiper

My edges are usually pretty good after the first firing. Although I do touch up the edges on the wet belt afdter the second firing. You are correct that the piece I showed earlier was 3 firings. One to fuse the base, one to fuse the border and the irid pieces and a third firing to slump. If I didn't want the border and mosaic pieces to stand proud of the base glass, I could do it with two firings.

Definitely consider working small... you can learn an awful lot about glass and how it behaves at different temperatures using small pieces...

As far as the electricity goes, I really didn't notice a spike in the electric bill... But then I don't fire every day depending on what other crises are happening in my life.

Tony

Thanks to all who responded to my question. I just wanted to close the topic by saying that I achieved the look I was after by doing a slump fire to 1220. The mold side was sandblasted and came out with a nice matte finish. A slight haze was present in one little area on the mold side but I think this had something to do with the blasting.

I hope to post this one soon because it is by far my best piece and would like to share it with you all.

thanks again for your guidence.
Dave

Thanks for the feedback Dave. It's nice to know when something works out.

Tony

Tony Smith wrote:Greg,

Are you talking about getting a matte finish or a fire polish? The piece I showed earlier was slumped ar 1250° and had what I'll call a sealed matte finish as opposed to the powdery frost that you get with a freshly blasted surface. I've been gradually lowering my temperature and now I'm down to 1150° for 15 minutes with a nice, uniform, sealed, matte finish (up or down) and picking up no texture from the mold.

Tony

Tony: I'm getting a powdery frosted finish. Now this is the side that is facing the mold (steel). On the side facing up always gets a nice matte finish. I was trying to make a base for a larger bowl. I put a disk of 1/8" fiber paper in the bottom - enough to get a dimple that the other bowl would sit in, so the mold side would be exposed. Can't seem to get a nice finish.

Hi Greg...

I would suggest increasing your slumping temperature in 25° increments until you see the blasted surface sealing. The difference is most likely proximity to the elements. I have a 23" Evenheat kiln with both side and top elements, and I prop the lip of my 15" bowl mold on 6" furniture so the top of the mold is only 3" from the elements. I also slump in ceramic molds which I sit on the kiln floor, but with those I use 1175° as a hold temp.

Tony