When does devit happen? & a flux question

[Cynthia]

I'm firing a public installation project for a client. It is 1/2" thick of layered BE red opal. He used Spray A as an overglaze, which is a low-melting ground glass with lead as a flux, for the first firing to laminate the glass. Top temp was 1350. and we crept up to 1350 at 100 dph. The piece is still in the kiln annealing, so I haven't seen how the Spray A matured at this temp...but...

We are going to bend this piece next using an even more conservative schedule of 70 dph to 1250 to achieve the bend. Will flash once it is fully bent over the mold. I have a couple of questions about the Spray A and when devit occurs in respect to the above schedule.

Since he used Spray A on the first firing, will he need to reappy for the bend? If he applied it from the get go, is the glass protected from devit for succesive firings, or will each successive firing need an overglaze? What are the temps that devit is most likely to occur within?

I have never used an overglaze (and never Spray A which is a flux) for bending and haven't needed to, but he is concerned that we are hanging about in the devit range for a long period of time, so better safe than sorry. I agree with the better safe than sorry, but will Spray A even mature at 1250? Can anyone tell me what the temp range is that it is supposed to mature? Are we even in the devit range at this temp, or does it have to do with how long I'm keeping this piece at this temp? We are bending very slowly because of the thickness and width of this piece to prevent it from splitting, so we don't want to speed it up.

Had he not suggested using the Spray A for the bend, I would never have even considered it. Now....He's got me wondering if I am forgetting something

I want to do right for him, but also don't want him to use the Spray A if it isn't going to mature and end up looking scummy. And if it isn't necessary, I am thinking leaving it off as being the safest method. He's on a deadline so we can't blow it.

Enough questions. Thanks for your input.

[Barbara Muth]

Cynthia, I haven't tried either yet, but our sponsor Fusion HQ has Super Spray which matures at 1350 and a bending glaze which matures at 1100. Roger Thomas seems to use the Bending Glaze a lot. Might be worth a try.

Barbara

[Cynthia]

I'd be more prone to using the bending glaze. I haven't had much success getting SuperSray to mature at that low a temp. I wonder if I can get my hands on some by tomorrow.

What temps do you need to get to for borax to mature? I've got that.

Good suggestion, thanks.

[Carol]

Cynthia

I recently slumped a float bowl at 1250 degrees. I applied borax overspray to prevent devit, and the borax did not mature but left a frosted look translucent top on what should have been a crystal clear bowl.

Carol

[Ron Coleman]

Just curious what kind of fuse you get with BE opal red at 1350? Sounds low to me.

You're right on the edge of temperature to get Spray A to mature. Depending on how long you soaked at 1350 it may have melted or may not. If the temperature was a little, short the piece will have a frosty to orange peel look.

Once you a have good layer of Spray A fired in place you shouldn't need anything else for the slump firing.

Ron

[Bert Weiss]

Cynthia

I am skeptical that spray A will look good fired only to 1350. I just had a conversation with Center de Verre Marty. He said that as long as BE is kept below 1375, he never gets devit. I fired my dichro frit tests covered with crystal clear frit to 1375, held for an hour and got clean tiles.

If Marty is right no overglaze would have been a better approach.

If the soray A comes out matte, fire again to 1400 to gloss it.

Bert

[charlie holden]

You're not going to get devit at 1250. You probably won't have to go to 1250 anyway. Fire up to 1150, take a look and raise the temp if it's not slumping fast enough.

Low temp oversprays are for getting a glossy finish on the surface at a slump temp. They are not for preventing devit at a low temp. In my experience devit happens when cooling down from a medium high fuse, not so much when only going up into the 1300 - 1400 range. When I cast pieces using Bullseye casting patties up to 1575, then cool down solwly, spending an hour or more between 1400 and 1300, I get very little, if any, devit. I only get it near the edges of the mold where there is dust. Of course red opal is a different animal than 1401.

What's the slump shape? Into or over the mold? What's the mold material? How big is the slab? These will all have an effect on the stress put on the pieces during slumping.

[Cynthia]

I just looked at it and it's glossy and just fine. Whew.

Now that we've survived this first firing, I will recommend he not apply the Spray A for the bend. I've never used an overglaze except for bending glaze for bending, so was a bit puzzled by his desire to do so. I've never gotten devit in a bending schedule. It's good to know that the temp is about 1375 for BE and we aren't going to fire any higher than 1250 (maybe lower).

The fuse you get at 1350 is simply a lamination with a softening of the cut edges...remains reasonably crisp yet a touch softened.

I'm going to order some bending glaze for future projects like this. Seems I might be getting a few more down the road and it could be a good overglaze for my work as well (except for that reaction thing).

When I fire for someone else, I prefer that they provide me with their schedule and we can tweak to match my kiln. I want to do right for the client, so if they want to do something that doesn't seem like it will work, I get a little squeeemish.

Many thanks for all the good info. I feel more confident about this next step now.

[Cynthia]

What's the slump shape? Into or over the mold? What's the mold material? How big is the slab? These will all have an effect on the stress put on the pieces during slumping.

The mold is a half orb, the glass will be draped over the mold. The mold is plaster but I don't know the composition of materials (he's the maker, I'm just the cooker). The peice is a 1/2" thick hour glass shape (red opal) on a base of machine rolled 6mm clear. The apex of the bend will occur at a weak point in the red glass, centered on the base. We are creeping up at a very low and slow rate to allow the glass to bend without tearing or splitting. I haven't seen his schedule yet, but will recommend a rate of 50 dph or less if he isn't being conservative enough, after a good soak at 1000. Will arrest once a full bend is achieved. HE's pretty conservative though, so doubt I'll differ with his schedule plans...we shall see...

[charlie holden]

The mold is a half orb, the glass will be draped over the mold. The mold is plaster but I don't know the composition of materials (he's the maker, I'm just the cooker). The peice is a 1/2" thick hour glass shape (red opal) on a base of machine rolled 6mm clear. The apex of the bend will occur at a weak point in the red glass, centered on the base. We are creeping up at a very low and slow rate to allow the glass to bend without tearing or splitting. I haven't seen his schedule yet, but will recommend a rate of 50 dph or less if he isn't being conservative enough, after a good soak at 1000. Will arrest once a full bend is achieved. HE's pretty conservative though, so doubt I'll differ with his schedule plans...we shall see...

This is what I would do. Lift the glass just barely off the mold, or just support the edges, by putting kiln posts under the corners of the hour glass. You don't need to put the kiln posts well under the glass. You can just barely put a corner under. You can also put some fiber paper on top of the kiln posts to soften things.

Watch it as you approach 1120. When you see that it has begun to slump over the plaster form so that glass beyond the thinnest part of the piece is supported now by the plaster, reach in and knock out the kiln posts. Sometimes the kiln posts will fall over themselves as the glass slumps off their edges. From there you just let the slump proceed as normal.

This method distributes the weight and minimizes the stress on the center of the glass.

[Cynthia]

Well, the project is finished. The first fuse was a success and the bend bent nicely. The red did devitrify though. My client hasn't seen it yet. Ugh. He applied Spray A to the red opal for the first firing, and didn't for the bend as per my recommendation. He was concerned that it would still devitrify because we were in the kiln for so long. He was confident that the Spray A would mature at 1250 because of the heat work factor (which is what I am assuming was in play for devit too). But I talked him out of it because I thought it would create surface problems.

Now that we're here, is there any way to remedy the devit easily and successfully? Or rather, is there anyway to put a glossy surface on this that will work? He doesn't have any red opal left and says he can't find any. His deadline is today, but I think that's out the window. Can Bending glaze cover devit successfully? It has to be glossy and be able to withstand the out of doors. I'm sure he is not going to be happy with the results or me.

I should never expect these kinds of jobs to go well. They just always seem to get ugly on me. I just got off the phone with him. He isn't happy. Ugh.

[charlie holden]

Well that's too bad. I'm sorry for you.

I can't offer much other than grinding or blasting off the surface, covering again thickly with an overspray and refiring on top of the mold. Back Magic matures at about 1000 degrees, but I've never gotten a truly glossy surface with it. I've never tried bending glaze. Maybe somebody else has another method.

If it were I, I'd give it the once over with 400 - 800 - 1200 grit diamond hand pads and see if they'll accept that finish. It is a very fine satin finish, softer even than blasting and fire polishing, but not glossy. I've fixed screw ups that way and had clients rave about how much they like that part. If they don't like it you can refire it.

I guess the lesson to learn is: when working with a new process or glass, do a test tile under the expected time and temperature conditions of the final piece and get the clients approval. If the client doesn't have time, he has to take on that additional risk.

Good luck, and treat yourself to some ice cream or something.

ch

[Cynthia]

Well that's too bad. I'm sorry for you.

I guess the lesson to learn is: when working with a new process or glass, do a test tile under the expected time and temperature conditions of the final piece and get the clients approval. If the client doesn't have time, he has to take on that additional risk.

Good luck, and treat yourself to some ice cream or something.

ch

Your sympathies are greatly appreciated. Fortunately my client was not irked with me; unhappy about the results, but not with my judgement call since he concurred. Still, what a let down. The client is going to put the piece on a wheel and polish it up since the devit is not very deep. He'll still make his deadline.

In the future, when in doubt I will trust my own insticnts. If I had I would have altered his schedule to fire more rapidly at the top to get in and back out of the devit range more rapidly. The bend was not huge, so the stress on the glass was slight. He wants me to fire some more panels for his installation, so I suppose he hasn't lost faith in me completely.

I had the same idea about treating myself to a little pleasure and walked to an ice cream joint this afternoon. Coffe ice cream with hot fudge and wipped cream. Yum. I'm feeling much better.

[Dani]

Just my 2c.... it's been my experience that you don't have to reapply overspray. It doesn't go away during fusing, it's there on the surface, and has always worked fine for me on subsequent firings even on a re-fuse. Haven't had devit problems at slumping or paint-curing temperatures so can't see that as an issue in post-fuse firings.

Not very helpfully yours,

Dani

[Brian and Jenny Blanthorn]

Well that's too bad. I'm sorry for you.

I can't offer much other than grinding or blasting off the surface, covering again thickly with an overspray and refiring on top of the mold. Back Magic matures at about 1000 degrees, but I've never gotten a truly glossy surface with it. I've never tried bending glaze. Maybe somebody else has another method.

If it were I, I'd give it the once over with 400 - 800 - 1200 grit diamond hand pads and see if they'll accept that finish. It is a very fine satin finish, softer even than blasting and fire polishing, but not glossy. I've fixed screw ups that way and had clients rave about how much they like that part. If they don't like it you can refire it.

I guess the lesson to learn is: when working with a new process or glass, do a test tile under the expected time and temperature conditions of the final piece and get the clients approval. If the client doesn't have time, he has to take on that additional risk.

Good luck, and treat yourself to some ice cream or something.

ch

I never do small tests

As they R just not like the real thing as the mass of the glass is different

I am no expert in BE but I think ur problem may B the opal is more prone 2 devit

Looking at the suggestions U might have been better going higher faster n flash heating the surface using

Baffle n Go technology

Or just sticking 2 what U did but using Baffle n Go

Thats assuming U were using side elements

A solution I use now with SLS is a realy slow sreap up 2 temp then fast cool when done

Another thing which realy seams 2 promote devit is opening the door

I try n avoid that

As I creates dust cooles surface which then reheats

But opal glass will already probably have neucleating points already in it

Where the hotter flash fire withy the spray A should have disolved

As ur well awair a lot of fun can B had with devit

[charlie]

I'd be more prone to using the bending glaze. I haven't had much success getting SuperSray to mature at that low a temp. I wonder if I can get my hands on some by tomorrow.

What temps do you need to get to for borax to mature? I've got that.

Good suggestion, thanks.

i havn't had good luck with borax muchunder fusing temps. 1450 or more is required.