Zinc or Tin Plate for Black Polishing?

[Tmuir]

I'm looking at having a go of the dark art of black polishing, in particular I want to learn it for restoring old pocket watches for parts that have suffered minor surface damage.

I'm going to cast and then machine my own polishing plate.

All the books talk about using Zinc for steel parts and I have read tin for gold parts, but online have read about a few people using a tin plate for steel parts.

Tin will be easier to cast than zinc, but I should still be able to manage to cast zinc, but just want to know if anyone here has tried black polishing and if so have they used a tin plate, or should I go the extra effort and cast a zinc plate?

[nickelsilver]

I have both and prefer tin. Some folks add a little silver to the tin (I've heard between 1-5%) for a little more hardness; I have a couple and also pure tin and can't tell a huge difference.

Just avoid lead or tin/lead alloy. The lead is toxic and its oxide is just abrasive enough to make polishing next to impossible.

What's more important than composition is that the block be flat and not too smooth (rough lathe finish or scratch it up with a file), and not too much polishing paste. It needs to get almost dry to hit the black polish.

[Tmuir]

Thanks, I plan on buying pure tin from a foundry in Queensland that sells it in small amounts to hobbyists for reasonable prices so don't need to worry about the purity.

With Zinc I would of had to gone done the path of green sand casting, but with tin I should be able to just get away making the mould with just getting some hardwood and using a hole saw drill a hole through the wood and clamp it onto  another bit of wood.

Yes the wood will likely smoulder a bit, but that doesn't matter for a one off use mould.

What diameter are your plates?

[nickelsilver]

I have a few around 100mm or so. Much bigger it's just more of a pain to redress them.

 

A friend who used to make them just melted the tin on a hotplate and poured into silicon molds. Another used shoe polish tins or tuna cans.

[Tmuir]

Thanks, I was thinking around 100mm, but its always good to get confirmation.

A silicon mould would concern me to use as its max temp is only 30C above the max use temp of tin, but I guess if you are careful it could be ok.

[Tmuir]

I ordered last Friday 3 kilograms of high purity (>99%) tin from a foundary, its currently in the post and should arrive late this week. (Cost a fortune)

Its my son's birthday this weekend so I doubt I will get a chance to cast the plates this weekend, but when I do I'll be sure to take photos of my whole process.

[nickelsilver]

I ordered last Friday 3 kilograms of high purity (>99%) tin from a foundary, its currently in the post and should arrive late this week. (Cost a fortune)
Its my son's birthday this weekend so I doubt I will get a chance to cast the plates this weekend, but when I do I'll be sure to take photos of my whole process.

3kg [emoji23] you'll have everything in a 1/2 mile radius polished. Joking of course, that's really cool. Do you have a tripod/bolt tool?

[Tmuir]

17 hours ago, nickelsilver said:

3kg you'll have everything in a 1/2 mile radius polished. Joking of course, that's really cool. Do you have a tripod/bolt tool?

I bought enough to make at least 3 polishing disks, so I can use different ones for different diamond pastes.

I have in the post a tripod tool for polishing flat parts, but not screw heads, if I cant find one soon for a reasonable price It will likely become a project for me to make one.