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first time using ceramic molds
Posted: Fri Apr 09, 2004 12:28 pm
by archie
Having never used a ceramic mold, a couple questions:
3 or 4 coats of kiln wash?
prefire to ??
how long before needing to kiln wash again
do you sand off when needed or can you actually rinse of kiln wash with water?
will most glass slump at app 1200 - 1250?
one more question, how the heck do you vacuum the kiln shelf without scratching it?
thanks, archie
Re: first time using ceramic molds
Posted: Fri Apr 09, 2004 12:39 pm
by Brock
archie wrote:Having never used a ceramic mold, a couple questions:
3 or 4 coats of kiln wash?
Or more. Make sure you can't see the colour of the mold through your kiln wash, that'll be enough.
prefire to ??
Pick a number. I fire high, others air dry.
how long before needing to kiln wash again
On a mold, firing low, sometimes a very long time. If the wash is chipping or spalling, redo it.
do you sand off when needed or can you actually rinse of kiln wash with water?
Depends on the wash, and the mix. I scrape and sand.
will most glass slump at app 1200 - 1250?
Yes.
one more question, how the heck do you vacuum the kiln shelf without scratching it?
Use the brush thingy accessory.
thanks, archie
Posted: Fri Apr 09, 2004 1:42 pm
by Sandi
Archie, also make sure that your ceramic molds have holes in them just like the regular glass mold do. If you don't the air between the glass and the mold has no where to go and you will get bubbles or possibly have a hard time releasing the glass from the mold.
Re: first time using ceramic molds
Posted: Fri Apr 09, 2004 8:59 pm
by Siyeh
archie wrote:
prefire to ??
do you sand off when needed or can you actually rinse of kiln wash with water?
500 degrees, 10 minutes
I hand rub/sand very lightly. I have never removed all the old wash from my molds and have been firing in some of them for 17 years with no probs. Usually I just slap a new coat on if I have fired too high (above 1275) or accidentally chipped the wash off.
Brenda Griffith
Siyeh Studio
\^^^^^^:/_ When you are up to your ass in ALLIGATORS It's hard
\\^^^\\ to remember that the original task was to drain the swamp!
Re: first time using ceramic molds
Posted: Sat Apr 10, 2004 8:14 am
by Sandi
Brenda
I'm glad to see that I not the only one that doesn't take the wash off my molds. I hate to waste something that might still be good. I always buy my molds in greenware stage than bisque fire them myself. The other day I was using a bowl mold for the first time and instead of slumping I draped over it. The mold cracked. Have you ever had them crack on you and have you fixed them. I do have some clay slip but not sure if that will work.
Sandi
Posted: Sat Apr 10, 2004 9:47 am
by Siyeh
A lot of my molds came from a potter I was in an artist's co-op with in the late 80's. He made them in a rough red clay--definitely not porcelain... maybe terracotta or stoneware?--and didn't fire them all the way because he said the porosity would work better for multiple glass firings. *Shrug* I am barely successful at the physics of glass so I just said "ok". Anyway, one of my favorit bowls had a big piece of the edge chip off in a move and I glued it back together with a clay patch I got at a ceramic store in Austin. It seems to be holding up fine, but I don't know how it would work with a finer grained clay (or if the grain even matters).
Re: first time using ceramic molds
Posted: Sat Apr 10, 2004 4:39 pm
by Cynthia
Sandi wrote:Brenda
I'm glad to see that I not the only one that doesn't take the wash off my molds. I hate to waste something that might still be good. I always buy my molds in greenware stage than bisque fire them myself. The other day I was using a bowl mold for the first time and instead of slumping I draped over it. The mold cracked. Have you ever had them crack on you and have you fixed them. I do have some clay slip but not sure if that will work.
Sandi
No need to replace primer on molds unless you fire high for some reason or it gets scraped or worn away...
It's a general rule of thumb that you shouldn't drape over clay because it does not contract as much as the glass will when cooling...which is most likely the reason your piece trapped the mold. (A shallow slope will work alright...like the sconce molds BE offers, but for the most part, draping over clay is dicey...) You can try using a defloculated slip to repair your mold. It will hold up, or not
. I've had mixed success with mending broken molds.
Priming bisque molds
Posted: Sun Apr 11, 2004 1:32 am
by Lauri Levanto
I make ceramic moulds for my back relief castings.
I use to apply the first coat of shelf primer before
bisque firing. It seems to last severaql castings @850-880 C.
I mentioned this before, and got replies that kiln wash
"degrades" in those temperatures. My experience, however, is the opposite, and my guess for the reason is
that the kaolin matures in those temps. When in touch with
fluxes,it starts to melt into glass.
When fired separately, there is no fluxes. The kaolin
is sintered into the mould surface,
"locking in" the alumina. During subsequent firings
the alumina wears of and needs replacement at some point.
-lauri