In article ,
Wes Stewart wrote:

Good to know. You might find that a dip in vinegar will help with the
removal of the black smut.

Thanks... I didn't know that! I often wondered if there was an easier way
to remove the black residue.

Actually, a stronger acid works better (quicker). The "blackness"
seems to depend on the alloy and it may still take light rubbing to
get the stubborn stuff off.

As I understand it, the black stuff is usually referred to as "smut".
It's the other metals in the alloy, left behind when the lye dissolves
the aluminum.

Anodizing shops will follow the lye-etch with a plunge into a "bright
dip" acid bath to de-smut the surface and leave it nice and shiny.
Bright dip mixtures seem to vary - one I've seen mentioned is mostly
phosphoric acid, with a few percent of nitric acid added. Kinda nasty
stuff.

Awhile back I heard that after the metal is finished in a lye bath then
boiled in a solution of color dye (RIT) a colored, metallic finish, can be
produced---one of these days I'll try it on a scrap piece.

Now you're starting into anodizing. See:

http://w3.uwyo.edu/~metal/anodizing.html

Yup. A common cycle seems to be: drill and sand, etch in lye,
bright-dip to de-smut, anodize to build up a porous layer of hard
aluminum oxide, boil in dye to color, seal.

One problem with the use of RIT color dyes is that they aren't all
that stable against UV, and can fade over time. There are
professional anodizing dyes which are more stable.

On simple projects I print or photocopy text then affix them onto to the
aluminum surface (after a first coat of acrylic on the aluminum) with white
glue then with multiple sprays of acrylic affix them permanently to the
surface. It worked real nice with a bandpass filter project---I secured the
graph of the filter characteristics onto the minibox for reference.

Nice idea. I use the ruboff lettering (Datak) but of course they
don't have any BPF response curves, [g]

The Brother plastic-laminated labelling tapes seem to work fairly
well, also. I usually use the standard black-text-on-white-background
and then spray with acrylic. The black-on-clear might look nice on an
aluminum case, but I haven't tries this myself yet.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
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