While I agree with most of the post (snipped away), the following
paragraph contains some wrong advice, with all due respect.

1) "Finish restorers" often contain many of the solvents used in
   lacquer thinner, which itself is a soup of thinners and solvents in
   proprietary proportions. The MSDS will tell you rough ratios. They
   usually only work on lacquer and shellac finishes, as the label
   will indicate. These are evaporative finishes and thus resoluble in
   their solvents. They work by re-amalgamating the finish, allowing
   you to remove the top layer of soil and dirt, and leaving behind a
   bit of the original finish, without the cracking and other
   accumulated problems.

2) Mineral spirits is _not_ a solvent for varnish. It's a carrier (or
   thinner). Once varnish is cured, it is not resoluble in its carrier.
   It's undergone a chemical change (polymerization / oxidation). Oil
   finishes work the same way when cured (cf. dried).

3) Soiling is of two types (see my prior post on this subject)

a) Those soluble in water, a polar solvent. This includes general
   dirt, food, body oils, etc. Often other chemicals, such as
   alkalines, surfactants, emulsifiers, and acids are added to assist
   the cleaning chemistry. In my experiece, this is the vast majority
   of soiling on wood.

b) Those soluble in hydrocarbons, non-polar solvents. This includes
   petroleum products (grease, oil, wax), inks, and some paints. These
   cleaners are typically called POG (Paint, oil, grease) cleaners.
   Mineral spirits and naphtha are two most common examples. D-limonene
   (citrus rind oil) is another.

4) Chronic exposure to chemicals, particularly acids in body oils, can
   chemically change a finish over time. Finishes can become gooey and
   soft and are no longer protecting the wood. An agressive cleaning can
   remove the goo. I always tell people at that point, I'm not removing
   finish, I'm removing the goo, the finish is no more.

Here is a site that explains some of the test procedures for "which
finish" is this: http://www.johnjacobmickley.net/Shop%20Pages/Tips%20&%-
20Info/Finishing/What%20Finish.htm

> From: Gary Roberts <groberts@l...>
>
> -- snip snip snip
>
> Same for finish restorers, which are often a simple mix of mineral
> spirits and one or another severely thinned varnishes. Their thrust is
> to slightly dissolve what finish there is and add a new layer of
> thinned film.
>
> What to do? What to do?
>
> Since we are talking about a family heirloom here, I would suggest the
> conservative approach. Spot test a seldom seen area with a cotton swab
> and mineral spirits, then alchohol. You're testing to see if the
> finish is shellac (alcohol) or a varnish (mineral spirits). Each
> solvent dissolves it's attendant finish. Once you know which is which,
> select the opposite solvent and gently clean the surface with a damp
> clean cotton rag. By this I mean use alcohol for varnish and mineral
> spirits for shellac.
>


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