[ Gordon Ramsey wrote in 190516 MMDigest:

> I noticed that about a quarter of the brass tracker bar nipples had
> significant green corrosion right at the end of the rubber tubing.

Hello Gordon,  I saw your post on MMD about corrosion on some of your
brass nipples.  Is it possible that the nipples have been exposed to
an acid?  For example, some solder flux which was allowed to remain
on the metal or on the tubing without being washed off?

Robbie suggested coating the brass with urethane.  That sounds like
a great idea, but before you do that, treat the metal with phosphoric
acid.  This converts the oxide in the corrosion to phosphor.  If you
just clean it off manually, without cleaning it chemically, some of
the oxygen molecules will remain bound to the metal and the corrosion
will continue under the urethane.

Here's the procedure:

1. Remove heavy build up of corrosion (probably none in this case).

2. Apply phosphoric acid with a brush or cotton swab.

3. The corrosion may vanish or turn dark.  If you are treating iron or
steel, the black color is iron phosphate, not iron oxide, and is safe
to paint over.

4. In some instances it may be efficacious to let it sit on the metal
and come back the next day.  If the metal appears clean with no visible
corrosion after a few minutes, go right to step 5.

5. Wash the surface with water to remove any white salt or acid residue
which may remain on the surface.

6. After washing, dry the metal quickly and completely with a hair drier
or a heat gun.

7. Immediately after drying, apply urethane; do not allow oxide any
time to re-form.

Phosphoric acid is available at Home Depot in a plastic one-gallon
container.  It is called "Kleen Strip Prep and Etch."  It is light
green in color and, in my experience, the store employees have no
idea what it is, so if you ask for phosphoric acid they won't know.

Steven Reed
Plano, Texas

 [ Vulcanized rubber releases sulfur compounds (e.g., carbon
 [ disulfide) which form green salts on the brass surface.  The easy
 [ treatment, I suppose, is to scrub with a solution of baking soda
 [ (sodium bicarbonate), then apply urethane.  -- Robbie