Dwight News ) writes:
I would like to clean up an old paddle.

1. Can I use the oxalic acid which I have had in a bottle for twenty years?

yes


2. What proportion should I mix

"Bleaching Wood

Oxalic acid, which comes as a white crystal, is one of the oldest
bleaching agents. It is used where a comparatively mild bleaching action
will suffice. Prepare this bleach by dissovlign from 3 to 4 ounces of the
acid in each quart of hot water. ... Several applications may be made
until the desired colour is reached. Then neutralize the acid by swabbing
the surface with a solution of 3 ounces of borax per gallon of water.
Finally rinse with hot water and wipe dry."

Note that iron in contact with oak will react with the tannic acid to form
ferric tannate, a black stain. Oxalic acid will change it to colourless,
water-soluble ferrous tannate which can be rinsed away.

"Ordinary chorine laundry bleach, a 5 to 6 percent solution of sodium
hypochoride, is the basis for a simple bleach suited to many woods. Mix 8
ounces with 1 gallon of water. Apply it liberally, then let it dry.
Repeat, if necessary, and then rinse." It's recommended for fungal stains
in sapwood, but not oak or poplar.

Source: Popular Science "Formuals, Methods, Tips, and Data for Home and
Workshop" (1969)

Since the oxalic acid is an acid and chorine bleach is a base they work by
different chemical reactions, using both (not at the same time) might do a
better job of bleaching out wood stains. I used chorine bleach and
sandpaper to try to clean up an old paddle with moderate success. The
classically-shaped refinished paddle with stains has a certain antique
something about it.

--
------------------------------------------------------------------------------
William R Watt National Capital FreeNet Ottawa's free community network
homepage: www.ncf.ca/~ag384/top.htm
warning: non-FreeNet email must have "notspam" in subject or it's returned