casting copper

[PeterG]

I need to cast some copper "nuts" (vegetation, not nuts and bolts...not the insane nuts either...I think..) for use in a sculpture that will incorporate some delicate blown glass. My understanding is that copper and glass will expand and contract at the same rate. I assume this means that the copper should be reasonably pure. I have only found information on casting copper alloys.

Does any one have any information on this, keeping in mind that I have never cast ANY metals before?

What is the best way of joining the cast copper parts to the larger sculpture given I dont want the colour change of silver or solder?

thanks again in advance..

Peter

[jviii]

Hi Peter,

My response here is in reference to joining Cu to glass, so it may be better in another thread. Cu and glass do not really expand at the same rate, but rather they can be joined because of the ductility of the Cu. What this means practically is that the section of Cu joined to glass must be quite thin so that the Cu can *flow* and move with the glass. For example, in a Cu-glass joint of tubing, the Cu tubing is thinned considerably before the two are joined. There are other ways to join different metals to glass, i.e. graded composition of the glass to acheive a more similar coefficient with the metal.

There are probably glasses available that can match expansion rates of Cu. My experience is mainly as a chemist using stock on hand. Others here may be better able to comment on the sculptural implications of these types of joints. This interface issue may or may not have bearing on your design, but I would hate to see your Cu nuts crack off at the glass-Cu interface when the heater or a/c kicks on.

Best wishes,
Joe V.

[warren01]

Peter, I am not a caster but I work a lot with copper. From the information I have gathered, copper is very hard to cast. There is usually too much porosity in the casting when done. You may want to go with bronze castings and then use a powder metal copper spray to give the copper look. This may also help to color your welds/solder joints. There are several metal sprays available, some will even go over plaster and resins. Check this website and review the information on powder metals.
http://www.sculptnouveau.com/


warren

[PeterG]

Thanks for the input guys.


Joe, the copper will be used to make a branching "cage" that glass will be blown into rather than being directly joined to the glass. Hopefully this will reduce the stresses a little.

Thinking about your comments, a beautiful delicate sculpture could be formed by merging thin tubes of glass and copper...

Thanks for the website Warren. I think I'll try a few of their products.

Peter

[coldcaster]

Peter.
I just noticed your post. I have cold cast copper and other powders many times with great success. You might want to check out this site.

I got some Copper powder from them that was wonderful and one of their sales people kind of walked me through a lot of questions I had. Good luck!
Thanks.www.material-resource.com (http://www.material-resource.com)

[Thatch]

Peter,
Is the copper going to be a nut shaped cage that glass will be blown to fill voids? I am having a hard time visualising what you are going for here. Back to the copper. You can get just about any guage wire that you want, it is easy to bend and there are a lot of good clear epoxies out there. Something to consider is that copper oxidizes fairly fast so you might need a clear coat.
Bronze was mentioned earlier. There are also bronze alloy rods, or wires available that are used in brazing and building armatures used in lost wax casting. Untouched it looks like dull copper and you don't have to worry about oxidation, nor the shine of clear coat. That still leaves you with how you want to make your joints and attach the glass.

My experience with copper and glass are limited to doing some 4"x6" enamel plates, and that wasn't easy because of the size.

Thatch

[nep75]

As someone mentioned before, casting copper is more involved than just doing bronze. It has to be heated with coke in the crucible so it melts right. It's been a while since I've done it, and it was only once or twice. I believe it needs to be degassed as well, that should help the porousity. But it's a lot more tricky and I wouldn't recommend it for a first time metal caster. How large are these pieces going to be?

That would really determine if it's possible or not. If you're thinking of melting 20 pounds of metal, then there are a lot of safety issues, plus the furnace and shanks and people to help and....... If you're going small then you still need to take safety steps but it won't be as tricky/scary.

I like the idea of using the metal of your choice rods and fabricating. There's even a metal coating that can be brushed on the joints if you don't want the soldered silvery look. Just a thought.

Sounds like it would be an interesting piece. :)
~ N