Glass sticking to ceramic mold.?
I was attempting to slump two pieces of previously-fused glass onto an oval shaped ceramic mold. When I opened my kiln the next morning, I saw that the glass is completely stuck onto the mold. I'd applied 4 layers of kiln wash to the mold, but it sat for about a month before I used it for fusing. Would that affect the efficacy of the kiln wash?
Obviously the glass is a total loss, but I do want to save the mold. Do any of you know what I can do to get the mold to release the glass? I looked this up in the archives, and I only saw SS molds addressed.
Thanks in advance for any advice you might have for me.
Just a few days ago someone posted with this same problem.
I think you can find some suggestions if you scroll down and check the posts for the last week or so.
* that's odd. what is the mold made of?
i purchased a greenware mold, sanded it down very smooth, and bisqued it a couple of days ago. i used it for the first time last night, and due to a brain fart, forgot to kiln wash it. not only did i not get any sticking, but got almost no surface texture even though i used a top temp of 1280 for slumping.
* That's odd! What is your mold made out of, Charlie?
* i don't know exactly. normal greenware slip, off white-ish clay body. it was very soft, so i could sand it with fine sandpaper to almost a shiny surface.
* How hot was your top temp in this firing?
I had a similar brain fart and neglected to rewash a kiln shelf after scraping off the old wash. I was fire polishing up a bunch of bits-o'-glass for inclusion pieces on the shelf while bending a few other pieces in molds. I just kinda forgot that I needed a primer on the shelf for the bits. The didn't stick and lifted off that shelf as if there was primer on it.
I've slumped into bisque ware molds with nothing but a product called "Free" by Unique Satellite dusted spariningly over the surface of the mold... I think it's nothing but talc, but at temps between 1200 - 1300F have never had sticking. I only did it for a while though once I realized it was cleaner and one less step to simply prime the mold that one time for years of bending pleasure.
* If the glass doesn't get "vitreous" enough, it won't stick to a mold or a shelf. I'm guessing, but I'd say below 1250 is certainly safe. We've slumped into unwashed stainless and that works at low temps. Not recommending it. Brock
* hmm. i'm curious, if glass isn't vitreous to start with, what is it?
Main Entry: 1vit?¡¤re?¡¤ous
Etymology: Latin vitreus, from vitrum glass
1 : of, relating to, derived from, or consisting of glass
2 a : resembling glass (as in color, composition, brittleness, or luster) : GLASSY <vitreous rocks> b : characterized by low porosity and usually translucence due to the presence of a glassy phase <vitreous china>
* It's a word we've come to use to denote glass getting sticky enough to grab foil or Paradise paint. Dictionaries are always behind, and new words and definitions come into being through usage. Brock
* My highest temp was 1300. So, none of you think the problem was the fact that the kiln wash was applied a month before the firing?
* I doubt it, I have molds that that the kiln wash is years old. Brock
* No. It's not about when it was applied. As Brock said, it's not a problem to have really old primer on a mold. In fact, once they're primed, you can use them repeatedly for years if the coating is intact.
You say you slumped onto this mold. Did you mean you draped it over? If that is the case then what you might have here is that the glass has traped onto the mold. The glass will contract more than the clay as it cools. It will squeeze the mold and often one or the other will fail...or you get a mold with glass wedged fimly onto it...Is this what happened? You want to slump into clay, and drape over steel.
Here are my other rambling thoughts...
What is your primer made out of, or who manufactured it? Have you used it on the shelf and other molds before...or is this a new batch for you?
You say that the glass was previously fused...by you? Do you know what the glass is?
Can you discover anything that was done differently this time than in previous times with either the glass or the primer?
Did you perhaps have an overglaze or overspray applied to the backside, such as Back Magic, Bending Glaze, Borax, Spray A, SuperSpray... Some of these, even if applied on a previous firing and matured, will stick to primer on subsequent firings.
I can't think of any other reasons why your piece would have stuck .
* That's not at all odd, Charlie. I discovered several years ago that the shallow clay molds don't have to be kiln-washed. I never tested the deeper ones to see if they would stick. I can't say I've noticed a difference in texture since the kiln-washed ones are pretty smooth, too, on those rare occasions when I don't have a granite bottom. So are you done with your maglesses since you're back with us?
* Ok, maybe thta's it! This was a very shallow bisqueware mold, and I did fuse the glass myself previously. I don't know what kind of glass it is. However, I DID apply Borax to the top surface, and I THOUGHT I was extremely careful to get none on the back. I'd totally forgotten about that. I guess it was the Borax. I haven't had time to try to salvage the mold yet, but am hoping to do so tomorrow. Thank you all so much for your input. Kay
* i was curious about this, so i've investigated this property. along with a bunch of scientific papers on the stickiness of things and why this occurs, i also asked corning about it. this is what they've said:
Thank you for your recent request, according to my contact, viscosity, is the correct term for 'stickiness' of molten glass, example molasses, tar etc. If we can be of further assistance, please feel free to contact us.
Kathleen (Kathi) S Johnson
Infrastructure Support Services
corning's term matched what i found in the papers. if anyone's interested in the links to the papers, please let me know.