Odd polishing problem

[ErichCDesigns1]

Greetings All!

I've encountered an odd problem with polishing that I thought I would pick your brains on.

I have been working on polishing some flat, sterling silver stampings after laser engraving. The stampings get in engraved and then jump in the pickle for a few seconds to remove oxidation. From there, they are polished. However, as I go through the process of polishing the stampings to a near mirror finish, no matter what I do (sand, bobbing compound, 3M wheels, etc.) the stampings polish out with a somewhat "frosted" appearance where the metal grain can actually be seen. To be clear, the surface is polished to an extremely flat finish (i.e. no scratches left). Yet, the physical appearance of the grain still shows up and creates a frosted appearance rather than a

"liquid-silver" or true mirror-like appearance as when anything else is polished. I've tried re-sanding, re-polishing, etc. and this routinely shows up. Has anyone else ever had this problem or know how to rectify it? In 14 years of jewelry work, this is a first to me and I'm honestly quite baffled by it.

Thanks for any help you can offer!
Sincerely,
Erich C. Shoemaker
www.ErichCDesigns.com

[Paul3]

huh - sounds just like it's been etched to show up the grain boundaries etc. could be the acid is etching the crystal structure, or especially the grain boundaries.

I encountered this sort of techniques when doing metallurgy at uni etc.

There are techniques for electropolishing that might restore a mirror finish - don't know how commonly available they are. Electroplating (or electro-less plating) might be easier...

[Paul3]

huh - sounds just like it's been etched to show up the grain
boundaries etc. could be the acid is etching the crystal structure,
or especially the grain boundaries. I encountered this sort of
techniques when doing metallurgy at uni etc. There are techniques
for electropolishing that might restore a mirror finish - don't
know how commonly available they are. Electroplating (or
electro-less plating) might be easier...

I've just remembered a silver plating technique used by my uncle (scientific glass blower) for backing mirrors. Uses sugar silver salts and ammonia to plate silver onto surfaces... a quick polish would be needed and I'm not sure how well it would stick - should be OK if clean... never done it yet.

[Charles_Allenden]

Hello Erich,

Without physically seeing the pieces it is hard to be sure but what you are describing sounds to me like an 'orange peel' effect caused by the annealing of the stampings after they have received

insufficient cold work. What size would you estimate the grain size you are seeing to be?

Charles