So last time we talked about casting pewter. Even though it is a fairly simple process it is definitely not instant. But what about casting bronze?
Casting pewter involves a simple mold, either soapstone or a modern material like silicone. But casting bronze is often done as a lost wax process. If you want to see more detail about the lost wax process itself I suggest that you read my six part blog series The Way That I Cast – Lost Wax.
But this blog is not about the casting process, it is about what happens when a cast piece comes out of the flask. This picture shows the beginning of the process.
On the left we see a freshly cast set of buttons, still covered with investment (the white layer). The next piece has the investment cleaned off, by scrubbing it with a brush in water. And then a fan of individual buttons has been cut off of the sprue button with the hacksaw (shown at the bottom of the picture). Then the individual buttons are cut off of the fan with the sprue cutters (at the top of the picture). What is left is a pile of buttons and a pile of sprue pieces.
The buttons have been cut from the small branches of the fan, and now they need to have the spot where they were cut off rounded and smoothed out.
And this is what I use to do that job, a wet sander. The sanding belts are made of wet-dry sandpaper. Water drips down onto the belts and cools the piece that is being sanded, while controlling the dust. Once the button sprue area has been shaped it is time to smooth it a bit more.
This set of Cratex wheels does a more delicate job of smoothing the area and removing scratches. There is a small pile of bodkins, crosses, Thor’s hammers, and dress hooks in process on the bench.
And once the general smoothing has been accomplished, the pieces are put into the vibratory tumblers to remove the oxides and further smooth the surfaces.
And this is what the vibratory tumbler bench looks like. There are two tumblers, each with their own source of circulating water. Each tumbler is filled with a different polishing material. The one on the right is the courser material and the one on the left is the finer material. The white bucket with the sieve on top shows the contents of the left tumbler being sorted to remove the pieces of cast metal. The cast pieces spend at least three hours in each of the tumblers, with a rinse in between to avoid transferring grit from one process to another.
And now what? Well, at this point I turn on a bright light, and check each piece to see how it is progressing. If it looks good I will set it aside for the next step in the process. If there are any issues, it will either be rejected if there are “fatal flaws” that can’t be cleaned up, or get a trip back to the Cratex wheels for some additional polishing.
Next Time: Are we done yet?