more casting mold questions

[Cher]

This is similar to Pauls question, but the results of my attemp. BTW, what product for making molds makes them reusable? If I hadn't gone so fast in ramping maybe? Anyways, here goes:


I made a shallow, open face casting mold using hydroperm.
"1 to 1, stir and pour. Sit 30 minutes then remove. Fire the mold at
300 degrees fahrenheit for 4 hours or more in a vented kiln to remove
any internal moisture".

I cast translucent glass frit: 1 was be cranberry, 1 be adventurine
green and 1 gna blue and they came out crusty and milky looking..
looked like hydroperm. I cleaned every way I could think of: brush,
elbow grease, dremel sander flaps, CLR. Could not get the glass clean
or clear. I fire polished as a last resort; somewhat clearer, but
still "dusted", white in crevices on the gna. What am I missing? I
could live with different texture or milky look, but this just looks
scuzzy and scummy. Any ideas?

Oh, if it matters, haha, the molds did crack shortly into the fire
routine, which was a rather fast ramp in a 6x6 evenheat. I coldworked
and fire polished the resulting seams.

[jerry flanary]

Pics?
The milkiness is from using frit, I believe. You might try the flowerpot technique to escape this...
I don't know of any mold that is reusable. At least not with any detail. you might be able to repeatedly cast a simple shape in a ceramic or ss mold but I don't know that it would really be cost effective unless you were casting, say, cow pies.

[Lauri Levanto]

Tanks Jerry,

Cow pies is a proper term for back reliefs I cast
into ceramic molds.

-lauri

[jerry flanary]

Sure, lauri. Glad I could help

But seriously, do you cast in them or just slump?

[Dennis Brady]

Ceramic molds can be used several hundred times, but probably the best material for multiuse casting is brass. If you can make a ceramic mold, it's not a big step to making a brass one.

If you want detail, you'll probably have to use some mechanical means to press the glass into the mold. Gravity isn't enough.
http://www.debrady.com/critters/images/starfish.jpg

[jerry flanary]

Wow Dennis, are you saying that you kiln cast those starfish in a brass mold? I would expect a product like that to be made by pulling a little ladle of glass out of a furnace and filling a graphite or metal mold. Then empty the mold when stiff and box it. But you are saying that you load the brass mold with frit or do you do the flowerpot over the top of the mold to get the nice clarity? Do you do a second slump firing to get the bent arms? How thick does the brass have to be to keep from warping from repeated hours of high temperature use?

[Dennis Brady]

Although we sell the starfish, we don't make them. Fella named Mark Lauckner does.
http://www.mayneislandglass.com

Recycled glass is melted in a small electric furnace and ladelled into a brass mold then press stamped to form the detail. Mark has designed and built a small glass furnace for casting (and sells videos on how to build them). Mark will be teaching at Victorian Glass Art Festival. Rick Smith will be teaching how to make brass molds.
http://www.victorianglassartfestival.com

At DeBradys, we're experimented with kiln casting scrap glass (or cullet) by placing a weight on top of the glass to "push" the glass into the mold. The amount of detail possible is determined by the amount of weight applied. Our goal is to kiln cast glass hulls for model ships like this. (we're currently using cast porcelain but would prefer glass).
http://www.debrady.com/masterartisan/im ... cutter.jpg

[jerry flanary]

Dennis,
That sounds pretty interesting. With the hulls, I wonder how it would work if you tried a slumping a thick sheet in the same situation instead of full fusing cullet. Experimenting w/ the thickness of the sheet could allow you to overcome whatever thinning that occured in the stretching. Thanks for the great response.

[charlie holden]

Ceramic molds can be used several hundred times, but probably the best material for multiuse casting is brass. If you can make a ceramic mold, it's not a big step to making a brass one.

If you want detail, you'll probably have to use some mechanical means to press the glass into the mold. Gravity isn't enough.
http://www.debrady.com/critters/images/starfish.jpg

So it's important to note here that Dennis is talking about hot casting, not kiln casting. Don't make a brass mold and try to kilncast into it. It will melt in your kiln.

ch

[Dennis Brady]

We tried making boat hulls by slumping into molds but the glass refused to go into the sharp points of the hull and the keel. We're now experimenting with both slumping and casting using a 3 piece mold - 2 sides and a top/insert. Some success, but still needs work. The key element appears to be how to get enough weight pressing down to force the glass into the mold crevice to form the keel and hull points. Slumping would be less work - it it can be made to work at all. It's easy to apply considerable weight to press cast glass - either hydraulics or a long-legged lever.


One benefit has come from all our experiments. The discovery that high volume use ceramic molds (for casting or slumping) cost surprising little to make.

[Dennis Brady]

We tried making boat hulls by slumping into molds but the glass refused to go into the sharp points of the hull and the keel. We're now experimenting with both slumping and casting using a 3 piece mold - 2 sides and a top/insert. Some success, but still needs work. The key element appears to be how to get enough weight pressing down to force the glass into the mold crevice to form the keel and hull points. Slumping would be less work - if it can be made to work at all. It's easy to apply considerable weight to press cast glass - either hydraulics or a long-legged lever.


One benefit has come from all our experiments. The discovery that high volume use ceramic molds (for casting or slumping) cost surprising little to make.

[Lauri Levanto]

Cow pies is a proper term for back reliefs I cast
into ceramic molds.

-lauri


Sure, lauri. Glad I could help

But seriously, do you cast in them or just slump? Jerry

I do both, but I prefer to cast. The reliefs are about
½" deep. A cast piece bends light more.

By the way. Sailships are one of my favourite subjects.
Last summer I made a series of The Tall Ship Race.

-lauri