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Brown stains as I polish. Is it a fire scale?

I got a ring casted in silver, and as I was polishing brown stain showed up everywhere. It is hard to remove and I was wondering what it is. I thought a fire scale is a dark stain, but is this also a fire scale? Does anyone know what this is and what’s the best way to deal with this? I’d appreciate it if someone could help me on this.

Thank you,
Young

Probably some sort of scale or stain. You might try the following: coat with borax and alcohol, burn off the alcohol, heat, but not to so that you can see any color, pickle and then give it a good soak in water. Do some light sanding or even abrasive wheel work if you can stand to lose the detail, then polish again. I get this from time to time on ingots that I have made and it is very hard to remove. Use an LED light or sunlight to see if it is still there. Good luck…Rob

Hi Young

Is this a ring that you cast or was it a purchase that you made and it was cast by someone else?

I have used boric acid and alcohol as a flux and fire coat for years. And it has reduced my experience with scale significantly. I think that from what I see in the photo you will need to sand that off. It looks pretty deep. As a last resort on jobs I couldn’t do over for one reason or another I have had some success with using a 50% distilled water and nitric acid dip to remove scale but it isn’t a sure thing and you run the risk of other damage to your work. The obvious precautions apply ventilation, eye protection, baking soda at hand, etc if you try the dip. I feel like I repeat this often but look into Tim McCreight’s book complete metal smith books. I would try again to abraid the scale off the work first and use the dip as a very last resort.

Don

Thanks for your suggestions! I tried alcohol and heat and it seems to have minimized the color issue on the detailed parts I didn’t want to sand. I’m glad it worked, great tip. Other parts I was able to sand off. Thank you!

Don,

I got this purchased from casting house. So unfortunately I won’t be able to try your suggestion. But As I mentioned above; alcohol and heat minimized the color. Thank you for your help!