Making Glass Bowl Molds

[archglass]

Someone has asked if we could make glass bowls for light fixtures - something we have not done before and I am uncertain on how to make the molds. All we have are drawings. These are various sizes, 24" to 48" in diameter and the height is about 1/3 the diameter. These start in the center with a slight curvature and are near vertical at the edge. 1/2" glass so a little heavy, with a small hole in the center. How can I make a mold of this size and from only a drawing? Stainless steel would work but who can make them?

Marshall

[Brad Walker]

These are called ball surface molds. They can be made from stainless (fairly expensive) or from clay. Some are commercially available, but probably not as large as you want. A good potter could make one for you from clay. Expect to pay $100 or more for the mold, maybe even double or triple that.

Also, because the glass will slide down the edges of the mold during a slump the molds will need to be larger than your final shape. For example, I have a stainless mold that's 22" across and 6 1/2" deep (smaller than the smallest one you want to make, but about that same 1/3 ratio) -- a finished piece in that mold will be 16 to 18" wide and around 3 to 4" deep.

Another option is to drop the mold through a ring and then cut off the top. That would be a lot easier to make a mold, but would probably require more coldworking.

Drill the hole after the slump.

[Buttercup]

Commercial woks from a restaurant supplier are quite large. I have one but it's still packed so I can't measure it but make sure it will fit in your kiln. Ask your client if they'll accept the dimensions of something already available as that will lower the production cost.

Here's a link to a site that shows sizes available:
http://www.foodservicewarehouse.com/edu ... 27572.aspx

You can then Google "Restaurant Suppliers" in your area.

Mine doesn't have the single handle. It has a rolled edge. Whatever the style the handles can be removed.
Jen

[twin vision glass]

Another option is to make your own molds out of MM6 or get a company like Zircar to create a mold for you. Expensive but it is really important for sizes like that to create a mold that will last for years BUT also will help to make a successful finished piece. Those are large sizes to be trying to create for sure and have a lot of logistical trial and error so make sure you are truly confident before you begin and the kiln is the right size , and that you charge a very large amount for the pieces. What is the liability for hanging lamps created that way. I never want to make people nervous , but at a conference once they did a whole talk on just that. Large hanging lamps. I do believe it was Walter Gordinar form Portalnd , OR who works with Uroboros often.
.http://www.uroboros.com/artist_detail.php?id=28
http://www.uroboros.com/artist_detail.php?id=38
Here was a topic talking about making your own molds that might help. Not the same configuration but solves a few things
http://www.warmglass.com/phpBB/viewtopi ... =3&t=41042

[archglass]

Thanks everyone, I appreciate the advice.

Marshall

[Terry Gallentine]

Quite a few years ago I was asked to make some 48" glass bowls using 1/2" plate. I made the assumption that I could fabricate a mold that would work out of some refractory material or clay. I spent a lot of time and some money trying to make molds. The molds were failing because of the weight of the glass. I ended up having a stainless steel tank fabricator make the molds out of stainless. It wasn't cheap but the molds did the job. There are two techniques for forming the stainless into bowls. One is called hydro forming (I think that's what they called it) where they secure the edges and bulge the metal with immense pressure. This technique is very consistent but is only used for relatively shallow forms. The second technique is that of spinning. This technique yields deeper forms but the walls are a little more irregular. I ended up backing out of the project when they decided they wanted to drill holes in the glass to hang them from rods. Some of the pieces weighed close to 200 pounds and the idea of them hanging 40" above people's heads and being weakened by drilled holes wasn't a liability I wanted to incur. This was around 15 years ago and refractory mold materials that would have worked may have been developed since then.

Good luck