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


#1

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


#2

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


#3

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


#5

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!


#6

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!