heating rate for easy glass flow

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suzanne
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Joined: Thu May 15, 2003 4:07 pm

heating rate for easy glass flow

Post by suzanne »

Hi there

I'm casting a shoe like form (real size, with about 1/2" walls on either side of shoe). I'm going to use the flower pot method ( suspend the flower pot full of glass cullet which was put in at room temp and heated at the same time as the mold)

With this method, I'm unsure how fast to take the glass and mold through the heating phase (from 900F upwards to about 1600-1650F) to make sure that the hot glass flows freely through the sides of the shoe (so the mold is not too cold and block the flow of glass)

Would holding the temp midrange for about an hour (at about 1450F) work?. Or does that produce other nasty side effects?

Cheers

Suzanne

PS. Love the new format for the board! :D
Colin & Helen
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Joined: Fri May 16, 2003 7:21 pm
Location: Albany Western Australia

Post by Colin & Helen »

And what glass would you be using ? when I use Gaffer Pb crystal if will start flowing at just over 825C from this point to the full flow temperature of 850c I slow the heating rate down Colin
Colin & Helen from the other albany<img src="http://members.westnet.com.au/sheltie/i ... b-logo.jpg">
suzanne
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Joined: Thu May 15, 2003 4:07 pm

Post by suzanne »

Hi Colin

I'm using gabbert cullet glass (not lead) ruby red. I believe the glass will start flowing at about 1600F-1650F. Just not sure how fast to heat it up from the 900F mark.

Suzanne
Colin & Helen
Posts: 44
Joined: Fri May 16, 2003 7:21 pm
Location: Albany Western Australia

Post by Colin & Helen »

suzanne wrote:Hi Colin

I'm using gabbert cullet glass (not lead) ruby red. I believe the glass will start flowing at about 1600F-1650F. Just not sure how fast to heat it up from the 900F mark.

Suzanne
Hello Suzanne I just can't get the hang of Fahrenheit.. but at the end of the day it's heat worked and as all kilns will not be the same ,testing and keeping notes is the way you should look at casting firings..As I.work in centigrade..someone who works in Fahrenheit may be your best bet with this question. I must admit I change the schedule as I fire..but my normal starting schedule would be 'take it slow' at 800c I slow the rate down to about 50c degrees pre hour( with flat fusing & slumping devet would be a problem) this gives the heat time to work.

So in short take you time and let the heat do it's work..

Colin

PS How do other caster work????
Colin & Helen from the other albany<img src="http://members.westnet.com.au/sheltie/i ... b-logo.jpg">
charlie holden
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Location: Atlanta

Post by charlie holden »

This is one of those questions that has to be answered by experience. How thick is the space for the glass to flow through? How well do you mix your materials and build the mold? My general advice is, if you're doing this for the first time, do it with a simple form that you can remake easily and retry after you've screwed it up the first several tries.

I would assume that you are familiar with holding around 1100 F to burn remaining chemically bound water out of the mold. You also need to ramp up slowly through the quartz invesion zone around 1040 F. Given all this, you're already going pretty slowly.

I generally hold just below the flowing temp to bring everything up to the same temperature -- 1500 F hold for Bullseye. But the rate between 1150 and 1500 isn't something I've given much thought to. I suppose you could get advice in either direction -- go slow to be nice to the mold or go fast so the mold doesn't have to stay very hot and continue to weaken over a long period of time. There are too many variables for one pat answer. Figure out what works for you.
suzanne
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Joined: Thu May 15, 2003 4:07 pm

Post by suzanne »

Colin

Thanks!

I agree with you on the the C vs F (but my kiln only speak F..hence...)

OK..that helps. So in F speak..go up fast to about 1472F then ramp at about 122F/hr until the glass flows. I will try this.

Cheers

Suzanne

PS. FYI the formula for C to F is ; C = 0.5555 (F-32)
S. Klein
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Location: Orange, CA

Post by S. Klein »

Suzzane: I don't put the glass in until the heat is up to 1500 for several hours (depending on the size and thickness of the mold) for BE or 1350 for Gaffer crystal. I find that the glass will start to flow while the mold is still gassing or not up tho the same temp as the glass. In some molds (depending on the opening for the glass to enter) a vapor lock will form and the glass will not flow in. Sometimes that lock will be deep inside and at times it will be at the top and glass will flow over the outside of the mold. The flower pot is glowing at this point and I am careful putting the first load of glass in if it is in chunks. After the first load of glass has melted, I just pory in as much as I can..............steve
Steve Klein Studio
1650 N. Glassell, Studio U
Orange, CA 92867
suzanne
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Joined: Thu May 15, 2003 4:07 pm

Post by suzanne »

Charlie and Steve

Thanks for the tips.

I was concerned about having the glass in the 900F-1600F range for too long (vitrification etc..). But it sounds like I have some play there to heat more slowly through that range than a traditional fuse.

Also for first time through I will probably cure my mold on a separate firing to get all the gases out so in case anything goes wrong I can remove that variable .

Cheers

Suzanne
davebross
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Joined: Fri May 09, 2003 5:01 pm

Post by davebross »

One more thing to consider.

That Gabbert ruby is a cadmium/selenium glass, which means it's a "striking" glass.

What this means is that the color happens by formation of crystals in the glass at a certain temperature. Any glass gets its color by subtracting certain wavelengths of light from what's reflecting or transmitting off or through it. The crystals are what do this in this particular glass.

The longer you stay at the striking temp. the darker color the glass will get.

Get it too hot and you get brown, which I don't think will happen in a kiln casting, you're not going that hot. Too short a time at strike temp and you get orange or too light a color. It also has a color density problem with being stretched too thin but that's probably not an issue with a casting.
Tim Lewis
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Post by Tim Lewis »

How long you take to get to melt point will also be determined by the location of your elements. For this purpose a top fired kiln could help the mold survive longer sit is farther from the element. Is is likely that your mold will be very weak if you take it up to 1600 F. Try to use a short time from 1200 so that the mold has less time/temp (heatwork) to weaken. 1550-1575 will probably be enough to do what you want. Let us know how it goes.
Tim
suzanne
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Joined: Thu May 15, 2003 4:07 pm

Post by suzanne »

Tim

I have a side fired kiln (old ceramic kiln). Also am layering on the investment to try to keep the thickness even. The specs I have on Gabbert glass (ruby red) is that it doesn't really start to flow out of the clay flower pot until about 1600F-1650F with a hold of a few hours. I used investment mix #3 from Dan Fenton's book which seems to hold together at higher temps and I have wrapped the mold with kanthal high fire wire to help hold it together. My kiln is just waiting to be outfitted with a vent so once that is in place I will give this a go and when it is done definitely let you know how it went. All the help from the experts out there is greatly appreciated. Muchos gracious, Suzanne
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