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Cold casting copper. - Dave Diaman - 02-12-2017
Here is something a little different. Once again not technically woodworking but it has its applications. Fairly frequently I'm asked to reproduce architectural elements or carvings. In most cases it makes far more sense to make a mold of the item I am coping than to carve multiple pieces. In this instance a customer had a cherub carving he wanted copied. They wanted several copies that would be painted and he wanted two with a copper or bronze finish. Here is the process I used for this one.
Here I am pouring a liquid silicone onto the original the customer provided to make my mold. In some cases the mold is much more complex. Sometimes this involves building a mold by brushing a liquid silicone one and then creating a multi piece fiberglass support shell. Other times I could be hanging 30' in the air applying a silicone very similar to silly putty to make a mold. The silicone is a two part mixture just like epoxy and once mixed has a limited work time. You have to order the silicone to suit the application.
Here is a photo of the completed mold after cured and after we have done quite a few castings.
The first ones I'm making are what is called cold cast copper. This is done by dusting the whole mold with a very fine copper powder. After the mold is dusted I then mix 35/65 copper powder and two part urethane plastic. I use a black dye in the urethane to keep the mixture dark. My kids love all the mold making and be have made everything from garden gnomes to backing and ice trays. He you can see one of my sons brushing the copper urethane in the mold to cover all the surfaces. This mixture cures in about 3 minutes but the copper has enough time to settle to the surface. Once the copper urethane mixture starts curing I fill the rest of the mold with more black urethane. This is in case I didn't get perfect coverage that the areas that show through blend in.
The casting can be demolded in about 10 minutes but I usually wait about an hour. The mixture generates a tremendous amount of heat and will actually burn you without protective gloves after 10 minutes. Here is what I have after it comes out of the mold. It basically looks like a chunk of chocolate.
I then take some steel wool and work the surface to make sure I have copper exposed. You can actually stop here. The more you buff with the steel wool the more shine the casting will develop. This one needs to look antique. There are quite a few ways to achieve this. The way I have found that I like best is to put the casting in a fume tank with a 28% ammonia solution. Hold your breath!
This is also the way I antique a lot of my brass to get an authentic ages look. 
After about an hour you get an even darkening of the whole casting.
Once I get this I then use a vinegar/ammonia/salt solution to wet the whole casting. As it dries you will have the characteristic tarnish the copper gets with age.
Once the aging is done you once again go back and hit all the high points with steel wool to expose the shinny brass. You can do a little or as much of this as you want. With this one I did a light buffing. This will allow the customer to pull it back more if they want to. Once the color is right you can cite it with a clear finish to keep the copper from tarnishing more again.
Here is a shot of my oldest son mixing a batch of the straight urethane with no copper powder. This product is almost water thin and clear until it cures. You can see in the photo how the part of the mold with the most mass and most heat is curing the fastest. The center of the mold that is only about 1/4" thick and edges are still clear. These areas will be the last to cure simply because there is not has much heat retained there. This stuff gets really hot when it goes. If I would have left the batch mixed in the mixing bucket it would have melted the bucket.
RE: Something a little different. - Herb G - 02-12-2017
Very nice Dave. Have you ever used Alumilite for casting?
RE: Something a little different. - Dave Diaman - 02-12-2017
(02-12-2017, 02:56 AM)Herb G Wrote: Very nice Dave. Have you ever used Alumilite for casting?
No, most of the products I use from come from Smooth On. They have quick shipping as well as a huge selection of products for different applications. They are expensive but just about everyone has high prices for modeling products.
RE: Something a little different. - MattP - 02-12-2017
(02-12-2017, 03:24 AM)Dave Diaman Wrote: No, most of the products I use from come from Smooth On. They have quick shipping as well as a huge selection of products for different applications. They are expensive but just about everyone has high prices for modeling products.
That is gorgeous work, sir.
RE: Something a little different. - giradman - 02-12-2017
Hi Dave - beautiful work and planning -
Dave
RE: Something a little different. - Carheir - 02-12-2017
Nice work Dave.. Say, did you get your Emmert together and mounted?
RE: Something a little different. - Wizard of Oz - 02-12-2017
Wow, that's really cool! Thanks for sharing.
Oz
RE: Something a little different. - Dave Diaman - 02-13-2017
(02-12-2017, 07:45 PM)Carheir Wrote: Nice work Dave.. Say, did you get your Emmert together and mounted?
I did get the vise sand blasted, cleaned, painted and reassembled. I went a little against the grain and painted mine blue. I didn't really care about keeping the color original as the vice will be a user and only needs to look good to me and I'm not a big fan of the factory gray. I don't have it mounted yet though. My bench top is about 5" thick so it is going to take some work to hollow out an area for the vise. I'm considering building a new longer bench top and just making it to accommodate the vise. Here is a shot of it before the dogs and cleaned up handle when back in.
RE: Cold casting copper. - RonB1957 - 02-13-2017
Thanks for posting. Live and learn.
RE: Cold casting copper. - Dave Diaman - 02-14-2017
You would probably be amazed at the number of woodworking related applications for cold casting metal. I have actually cold cast brass hardware patterns that were not available for purchase anywhere. I made a polycarbonate copy of the back plate for the hardware using a photograph and cold cast the back plate using brass powder. I bought the appropriate brass bail and posts since there are not that many variations on those and did the antiquing process for them together. When I was done I had an exact copy of the original and the only one who knew they were not all brass myself and the customer. Normally this isn’t something I would do but the quote for having the brass custom cast was way more than the customer was willing to spend. In the end we would have had as much in the hardware as they had in the piece of furniture so this was a good option in this case. I'll see if I can dig up a photo of the hardware and post it later.