[Jewelry making - Article 00295] - Re: [Orchid] Best solvent for Shellack?

[Peter W . Rowe]

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>        I'm really not just trying to be difficult-- but-- of course,
>     the organic matter doesn't "disappear"... it breaks down into
>     smaller bits, or recombines, or... what? Dissolves? That kinda
>     sounds like what a solvent does to me. So, if not, then what is it? 

    Solvents, Noel, are materials in which other materials can be
    dissolved, or evenly mixed.  The key here is that dissolving the
    other material does not destroy it.  Only separates it into separate
    ions or molecules of that material, floating around in the solvent. 
    If you allow the solvent to evaporate, you then get back the original
    material in it's original chemical composition.  Example: dissolve
    salt in water, it "disappears".  Evaporate the water, you again have
    salt, undamaged.  Dissolving a material does not involve an actual
    chemical reaction, and does not intrinsically change the chemistry of
    the material that's dissolved, only it's physical form, from which it
    can be again extracted. Some other examples:  Carbon dioxide gas can
    be dissolved in water, and can be easily extracted again (if there's
    enough, you only need to shake it to get some out, as in a can of
    Pepsi).  In our work, silver can be completely dissolved in gold, or
    gold dissolved in silver.  Normally they are molten when this
    happens, but that's not actually required, if you consider the
    mechanism of diffusion welding.  The solid crystals formed in such
    solid solutions are even mixes of the two metals, which
    interchangeably take random places in the crystal structure,  the
    same structure that would exist were it just one or the other metal. 
    Copper, on the other hand, is not totally soluble in silver when
    solid, but IS so, when both are molten.  So when the metal
    solidifies,  it segregates into two or more distinct crystal
    compositions, with varying amounts of copper, and as it cools, the
    structure is less and less stable with even those mixes.  it's that
    fact that allows precipitation hardening of sterling silver, since
    extended heating to below the annealing point allows the
    "uncomfortable" super saturated percentages of copper to migrate out
    of solution in the silver to along the crystal boundaries, where it
    forms separate copper rich crystals.   But in all these cases, the
    hallmark is that even in solution, the essential chemical identity
    of the dissolved material is preserved.  In addition, the solvent
    itself is also not changed by the process, and also can be separated
    again from the solute (the stuff dissolved in it.) 

    Sodium Hydroxide, by contrast, does not do this, at least not in the
    examples cited.   It actually reacts chemically with organic matter,
    destroying the chemical bonds that hold the various proteins, etc,
    together, resulting in not just other chemicals formed from the
    broken proteins, but other chemicals formed when the sodium hydroxide
    reacts to form those other chemicals.  Yes, the organic matter
    "disappears".  But you cannot get it back.  Both the organic matter
    and the sodium hydroxide have been chemically changed by their
    interaction.  Another familiar example is that food is not dissolved
    in your stomach acids.  Instead, it is digested, broken down from
    it's original form into simpler proteins that your body can then use. 
    You cannot take it back out of your stomach and get the same food
    back.  As we all know, the next time we see what's left of the food
    we eat, it looks rather less appetizing... (grin) (sorry 'bout that
    image.  Couldn't resist...) 

cheers
Peter Rowe 

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