[SEL] Patina on Brass

[Rob Skinner]

This weekend I finished making some parts, one of which was
in brass.  It came out nicely, except that it looked like
bling hanging from Fiddy's neck rather than something that
belongs on a rusty old engine.  
 
Afflicted with Manic-Obsessive disorder, I had no time to
wait for patina the old fashioned way.  Something had to be
done, and it had to be done NOW.  
 
The goal was to expose the brass to chlorine to get it to
change color.
 
Previous experiments with bleach (sodium hypochlorite) took
a long time and were less than impressive.  Where to get
more chlorine?  Need more chlorine...  
 
I've also used muriatic acid in experiments, but it hasn't
been particularly useful in creating a patina.  
 
By now any chemists reading this can see where the story is
going, and the sensible ones are shaking their heads in
disbelief.  They're right.  If you value your health, you
should hit the "delete" key now.  What you're about to read
is something that can very well get you dead, or at least
make you blind and burn holes in your skin.  
 
Anyway, in a deep plastic container was mixed a little
bleach with a little muriatic resulting in a BIG fizzy
reaction.  It was evident why this experiment is frowned
upon by experts.  
 
Industrial quality protective gear is very good idea here:
gloves, goggles, face shield, respirator and ventilation
hood at the very least.  
 
The brass part on the end of a wire dangled in the plastic
container IMMEDIATELY started to turn color.  I accidentally
dropped the brass into the broth and all the color dissolved
away.  Back out of the mix and it started turning color
again.  Within a minute it was a very dark brown.  Most
washed off, leaving a pleasing patina behind.
 
I used a couple ounces of each ingredient, but suspect that
a teaspoon or tablespoon of each would have been sufficient
to make the quantity of gas needed.  It's heavier than air,
so you don't need to worry about losing it out of your
plastic container.
 
If you use this technique, keep in mind that you're
manufacturing poison gas -- chemical warfare gas.
Seriously.  It's a tool that can help you make cool stuff,
but like other tools in the shop, can be dangerous if you're
not paying attention.  
 
Start with small quantities, and by all means keep the large
jugs of ingredients far from the other ingredients.  I'd
venture to say that if you accidentally spilled both
containers on the floor in your shop, the resulting reaction
would create enough gas that you wouldn't have to worry
about what's for breakfast tomorrow.   
 
Have fun, play safe, make pretty engines.
Rob