Metallurgical learning

[jarkman]

In today's lesson, we learn that silver/copper, 50/50, comes out looking remarkably similar to tin/copper, 10/90.

In this way, an expensive metal can be used to simulate the appearance of a cheap one. Ho hum.

Comments

[e_spy]

Ah, but the potential palette is going to be very different, isn't it? Inlay one with the other, patinate both... Quite surprised at the description - I would have expected it to be a fairly silvery alloy.

What was the drive behind making a more expensive shibuichi?

[jarkman]

Well, I am a bit puzzled today.

I did a bit of casting yesterday, with the two alloys, and my initial reaction was based on the colours of the fesh-sawn ends after I cut the sprues off.

But today, the Ag/Cu sprues are a very pale yellow, and the bronze sprues are much copperier. I don't know if that's down to a change in the lighting, or changes with a bit of oxidation. My bet is on oxidation.

Furthermore, the surfaces of the cast Ag/Cu objects are silverier than the sprues, even in the places where I cut the sprues off. It's as if the finishing and polishing has hidden the copper. At first sight, I'd think they were just sterling.

My aim was a pinkish silver colour, which I've made in the past on a testpiece. But this has come out different...

[e_spy]

It wasn't hot still when you desprued, was it? I've seen a yellow colour on the surface through oxidation when I've done that with silver. Any chance you've not got full mixing of the alloy during the superheat? Worst case, it may be worth remelting and recasting...

Really ought to use my vacuum caster some time soon - having too much fun beating up sheet metal though.

[jarkman]

No, it was cold when desprued, and I stirred it with a stick when it was hot. I think it must be to do with the colour being less visible on the polished surface.