The black art of black polishing

[Steve CrowParticipant @stevecrow46066]

As anyone done any of this?

All the descriptions I've seen call for a zinc or tin lapping plate.

I presume the reason for using a soft metal is that the diamond granules embed in the surface so the plate doesn't get abraded, only the work piece. Or am I wrong on this?

I can't find suitable zinc or tin anywhere. Is there another non-ferrous metal suitable? Maybe a grade of brass or annealed copper?

I've also heard of people getting good results using lapping film stuck to float glass.

Any help or advice would be greatly appreciated.

Steve

[Steve CrowParticipant @stevecrow46066]

[roy entwistleParticipant @royentwistle24699]

It is usually the plate for mixing that is tin or zinc. I have seen plastic ( credit ) cards used. Note the medium is Diamantine not diamond and is mixed with very little watch oil.( nearly dry ) The polisher must be softer than that which is being polished ( I have seen boxwood used ) and everything must be scrupulously clean. I believe Diamantine is an oxide of aluminium

Never done it myself, but seen it done

Roy

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Steve Crow on 10/09/2017 13:56:10:

I can't find suitable zinc or tin anywhere. Is there another non-ferrous metal suitable?

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Pewter is a reasonable alternative to pure tin

… have a look round the Charity Shops and Car Boot Sales, for scruffy old tankards, etc.

MichaelG.

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P.S. … May, or may not, be quite what you have in mind, but this is a very good introduction to the subject:

http://www.southbaytech.com/appnotes/54%20Lapping%20&%20Polishing%20Basics.pdf

Edited By Michael Gilligan on 10/09/2017 16:57:30

[RRMBKParticipant @rrmbk]

EXPLAINED: The Fine Art Of Black Polishing AKA Spéculaire

Have a look at this Steve its something that fascinates me as well,I seem to recall there was an older thread on here which gave a link to an old publication with details of a simple polishing jig.

Kind regards

Brian K

[ChrisBParticipant @chrisb35596]

If you use a 3000 – 6000 whetstone and finish on a leather strop with fine stropping compound you'll get a mirror finish. I normally use this process for knives but works well on other things.

[john carruthersParticipant @johncarruthers46255]

for telescope mirrors and lenses I use a pitch lap. (not the roofing kind).

Optical pitch is crud* free, less chance of a scratch on the work. You pour a layer onto a glass backing plate and press it to shape overnight, curved or flat.
Scribe a few channels into the surface to let it work.
If it's too soft scrape it off and boil off some of the volatiles to harden the pitch.
It slowly flows and adapts to the surface being worked, usually with a thin slurry of tin oxide or rouge.

*technical term.

[Neil WyattModerator @neilwyatt]

Why not buy lead free plumbing solder? 99% tin with a bit of copper, you can easily melt it and pour onto a suitable flat surface inside a ring to create a large flat plate, then back with plaster.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Neil Wyatt on 11/09/2017 10:20:14:

Why not buy lead free plumbing solder?

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Only because secondhand Pewter [even the shiny modern stuff if you're woried about Lead] is usually cheaper.

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by RRMBK on 10/09/2017 21:32:09:

EXPLAINED: The Fine Art Of Black Polishing AKA Spéculaire

Have a look at this Steve its something that fascinates me as well,I seem to recall there was an older thread on here which gave a link to an old publication with details of a simple polishing jig.

Kind regards

Brian K

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Excellent link, Brian

Thanks for sharing it.

MichaelG.

[Steve CrowParticipant @stevecrow46066]

Posted by RRMBK on 10/09/2017 21:32:09:

EXPLAINED: The Fine Art Of Black Polishing AKA Spéculaire

Have a look at this Steve its something that fascinates me as well,I seem to recall there was an older thread on here which gave a link to an old publication with details of a simple polishing jig.

Kind regards

Brian K

Thank you I have seen this, it's one of the better descriptions I've seen. Interestingly, there is no watchmakers lathe involved. When it comes to bevelling and polishing the circumference I'd be happier using a lathe than a jewelers burr.

Cheers

Steve

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