Howdy:

Its been a common practice with me to finish the aluminum surface of a
chassis or box with an immersion into a caustic solution followed with a
coating of clear acrylic spray---I like the satin finish it produces. I
normally use lye that I regularly found on the shelves of our neighborhood
hardware stores. However, I've been having a harder time of finding the
flaked lye that I have used over the years for that purpose. I have used
'Lewis Red Devil Lye' that I found at Ace Hardware.

A project that I am currently working on made me think of trying a
substitute for lye with an item that I seem to find everywhere. Often found
in the automotive stores is a product that is referred to as a
'cleaner/degreaser' or 'heavy duty industrial cleaner'. I have seen it
marketed as 'Purple Stuff' yet I purchased a gallon called 'Right Stuff
(Purple Stuff Concentrate)' manufactured by Sunbelt Chemicals, Palm Coast,
Florida, 386.446.4595. Nevertheless, the contents of both bottles have a
characteristic purple color and contains (besides sodium hydroxide) a
component derived from citrus---but more importantly, the label states that
the product is NOT TO BE USED ON ALUMINUM!

I finished the surface of both halves of a mini-box by immersing them into a
solution, by volume, of 1 part 'Right Stuff' to 8 parts warm water (I used
1:8 for no particular reason---It just happened that way). The surface of
the aluminum began to bubble rapidly, but not uncontrollably, causing a fine
white froth to appear on the surface of the solution. I let the mini-box
soak for 30 minutes whereupon I removed them and placed them into a bucket
of water. I found that the removal of the black residue is easier to
achieve if I wash the aluminum parts while they remain under water---a
sponge or cloth works fine and a Q-Tip removes the residue from corners. I
observed that as the reaction proceeded the purple color of the solution
became clear.

Needless to say, I am entirely satisfied with the results. The dilute
solution of 'Right Stuff' provided a uniform satin finish identical in
appearance to a solution of lye (sodium hydroxide). If you can't find lye I
suggest a solution of industrial cleaner possessing caustic properties. The
next time I use 'Right Stuff' I will increase it by 1 part just to see the
result. The reaction liberates hydrogen gas---use adequate ventilation.

RG