Here is the recipe for whiting and gum arabic through the courtesy
of Organ Supply Industries (OSI).  I called Dennis Unk, CEO of Organ
Supply Industries, and he said it would be fine to publish the recipe
on the MMD.  In fact he expressed appreciation for the fact that I did
ask.

Bob Oppenheim

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Sizing Recipe

Mixing of sizing used in the organ pipe soldering process is an
imprecise science.  What follows are generally accepted guidelines
for the mixing of ingredients.

1. Gum Arabic Solution

Fill a suitable mixing container half full with Gum Arabic.  Slowly
stir in hot tap water by hand until the solution is of a thick, smooth
consistency similar to honey.  Stir well every hour or so over a 6- to
8-hour period.  Let the solution stand overnight to allow air bubbles
to rise to the top.  Remove foam from the top of gum solution.  The
solution is now ready to use.

2. Sizing Solution

Place six parts of powdered whiting in a suitable mixing container.
Slowly stir in five parts Gum Arabic solution.  Slowly stir in enough
room temperature water to thin this mixture to a paint-like
consistency.  An electric hand drill with a mixing attachment works
well.  The solution is now ready to use.

3. Application

Zinc Pipes: Dilute Gum Arabic Solution by 1/2 (one-half) with water.
Rub on evenly and let it dry.  Zinc is now ready to seam and solder.

Spotted Metal Pipes: Paint the mixed Sizing solution on a tin-lead pipe
surface with paint brush.  Rub the Sizing into the surface with the hand
until the Sizing turns dark.  Apply a second coat with a brush and let dry.
The metal is ready to seam and solder.

From:
Organ Supply Industries
2320 West 50th Street
Erie, PA  16505-0325
(800) 374-3674