Black spots in aluminium after annealing.

[ralaco]

To annealing my aluminium I used this method:

I wave the (acetylene or butane gas rich) torch over
the aluminum and cover it with smoking black soot. And
then proceed heating the aluminum until all the black
soot is gone, and the molding gets very bendable, but:

I got some burned black spots after annealing the
aluminium mouldings,
I only could erase the black spots by sanding and
polishing them but, it is too much work and too much
shining.

How did others do to annealing without these burned
marks?
Or
How to erase these burned marks without polishing?



Raul

[norm perkiss]

Raul,
I used a candle to soot the aluminum and a propane torch to anneal it. I kept the flame moving constantly, heating the metal just until the soot disappeared. I didn't need to clean or polish. I believe the trick is in the constant motion for an even heat?
Norm

[mercy]

i got extra aluminum and waited until sundown. i then cut a chunk of the extra and destroyed it with the torch. then i laid out my real piece, and torched it until just before it looked like it was going to do the same.

for me, it was easier to figure out what not to do with it by doing what i wasn't supposed to do with it and going from there.

[toypusher]

Raul,

Try cleaning the aluminum of all grease (ie fingerprints, etc) before the annealing process. Then wear gloves to keep oil from your hands away from the metal. I don't know if that is what caused your problem, but it may have been somekind of contaminate on the metal that created the black marks. I had a couple of really small problems like that when I did not clean the stickers off completely on a couple of pieces. Also, try using a candle and put a very light coating of soot on the aluminum.

Hope this helps.

[madjack]

Raul,
Also, try using a candle and put a very light coating of soot on the aluminum.
Hope this helps.

That is what I was thinking...that the acytelene put too much soot on the Al...used the candle method with a very lite coat of soot...contaminate could also have been the culprit, however we didn't take any particular precautions in that regard and had no problems and it was summer in the south when it was done(read lottsa sweat).....also remember the heat point at which the soot disappears and the Al starts to blister is very small
madjack

[ralaco]

Norm, courtney, Kerry & madjack

Thank you very much:

I will try both to clear the aluminium from contamination and to use the candle method with a very little coat of soot.



Raul