[Jewelry making - Article 00076] - [Orchid] Black residue with Ferric Nitrate

[Dave Sebaste]

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    Hi Folks, I'm stumped!  I'm trying to do something relatively simple
    I've done in the past, but am now having complications. 

    I have some 22k/sterling mokume gane sheet. I'm trying to lightly
    etch the silver content with ferric nitrate to provide a texture
    contrast... lightly frosted white next to the highly polished 22k
    gold. A very elegant look when it worked before. 

    Now, on a the last couple pieces, a durable black substance is
    developing on the silver. I have tried pickling, ultrasonic and ionic
    cleaning and nothing has removed it. It appears that it did etch,
    however. I mixed a fresh, stronger batch of acid using distilled
    water. I have used metal from two different batches of mokume. The
    last one was in the bath for only five minutes, and the black residue
    was already forming. I put my vibrating tumbler on top of the
    assembly containing the bath in order to provide some agitation. 

    Does anyone have any clue what is going on here, and/or how I can
    avoid the blackening and just get a nice clean etch? I don't have any
    nitric acid at my disposal at this time. 

    Thanks in advance! 

Dave
Dave Sebaste
Sebaste Studio and
Carolina Artisans' Gallery
Charlotte, NC (USA)
dave AT sebaste.com
http://www.CarolinaArtisans.com

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