advice needed on making a lightshade mold -

advice needed on making a lightshade mold

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Richard Dubois
Posts: 22
Joined: Sun Jun 22, 2003 8:10 pm
Location: SF Bay Area

advice needed on making a lightshade mold

Postby Richard Dubois » Sat Aug 30, 2003 8:26 pm

I am attempting to replace the ceiling lightshades on new fixtures we got for our kitchen remodel. The commercial shades are 12" across and 2.5" deep. They have a 0.5" flat rim that is captured by spring-loaded holders (look like C's). I need to make 4 of these shades.

I made a mold using Type B mold mix (I think it was Type B) - it was 25 lbs of mix poured over the commercial shade into a plastic stepping stone mold (with a cardboard dam to allow a taller pour).

After a week's drying, I fired the mold to 300F for an hour and then to 1500F for an hour. Then kiln wash. I slumped one test shade in it and found many hairline cracks radiating out of the center. Hoping they were just surface cracks, I was going to paint a slurry of new mix to fill them in, but the mold disintegrated when I carried it away from the kiln.

In addition, the slumped shade was cut to the full width, including the 1/2" rim, but the glass just folded up into the mold and there was no flat rim.

So, two questions - how can I make a durable enough mold to make my 4 shades; and how do I get the 1/2" rim? I'm guessing that some amount of oversize will result in a flat rim. It could be trial and error to find the minimum oversize to get the closest rim and then grind or saw out the rest.

Here is a pictorial history of the attempts so far:

[url] ... model2003/

Posts: 24
Joined: Sun Mar 09, 2003 3:24 pm
Location: Louisiana

Postby Melodie » Mon Sep 01, 2003 4:16 am

I’ve never used that type of plaster so I really can not comment on it. I would think that if a commercial slumper is not available in that size then it might be best to contact someone in your area that does pottery that can throw a bowl that size (not sure about a flat rim but want to say that a good potter could achieve one) or someone that does slip casting. A mold that size shouldn’t be very expensive, especially done locally.

If you have access to Lundstrom’s first book he shows placing a second ring mold on top of the glass to keep the rim from slipping in. This could possibly be weighted down even further if needed. Can’t guarantee results, I’ve never tried it but thought it might be worth a thought.


Laurie Young

Postby Laurie Young » Mon Sep 01, 2003 4:57 am

A good potter should be able to throw this shape, maybe lay out glass a bit larger than you need and then cold work to fit, they are fairly shallow so it shouldnt slip into the middle, go up slow and slump at a low temp. Plaster molds dont tend to last very long, but having said that I have used ceramic slip molds for multiple firings.

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