[Jewelry making - Article 00060] - Re: [Orchid] I must be getting too old for this.

[Alden & Glenda Blood]

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    Hello Bruce and the responders to this thread.  Fluoboric acid could
    be an effective pickling agent for the alloys containing silicon
    that have been giving problems with soldering.  Fluoboric acid
    (HBF4) is used in commercial processes for cleaning metal before
    electroplating.  The acid is effective in removing oxide and
    silicate films that may be on the metal surface.  The ability of
    fluoboric acid to dissolve silicon materials is confirmed in section
    K of MSDS 6008 (General Chemical Corporation) where it is noted that
    the acid is corrosive to glass, ceramic and metals.  Noble metals
    are not attacked by the acid to any appreciable extent.  Fluoboric
    acid/hydrogen peroxide mixtures have been recommended for removal of
    soft solder in at least two publications (B. Knuth, Jeweler's
    Resource, First Ed., Jewelers Press, p. 46 and Oppi Untracht,  Metal
    Techniques For Craftsmen, 1968, p. 182) Please note that Bruce Kunth
    confirmed a typographical error for the name of the acid.  That
    error has been corrected in the 2000 edition.  He has used the
    fluoboric acid/hydrogen peroxide system for soft solder removal from
    gold jewelry and found it satisfactory. 

    Fluoboric acid is provided as a 48% solution in water.  It is stable
    but should not be boiled.  If silicon forms a layer on heating as
    suggested by James Binnion, it might be necessary before soldering
    to heat the work to near soldering temperatures, cooling in standard
    pickle and then dipping in the fluoboric acid.  The acid does not
    appear to be any more hazardous or difficult to work with than the
    other strong and corrosive acids frequently used, based on the
    information in the MSDS.  It surely is not in the same class as
    hydrofluoric acid.  One source for the acid is Chemical Associates
    in Pennsylvania.  They quote a price of $26.03 for a liter of the
    48% solution. 

    This is just a suggestion.  I have not tried it.  The information
    available suggests it should work if silicates are the cause of the
    problems cited.  However, there sometimes is a "slip twix the cup
    and the lip" so a trial should proceed with caution  I have not had
    the problem so far even although 90% of the repair work I see is
    10K. 

Captain Blood
"Marlinespike Seamanship in Precious Metals"
mariner AT tgtel.com


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