ATM Melting pitch

["mlbrown@everstrive.com" <mlbrown@everstrive.com>]

>>A question on melting the lap though,  can I melt 
>>this in a clean tin can sitting inside of hot water on my stove for a few 
>>hours?  kind of like a double boiler for making fudge candy.  has anyone 
>>tried this?  honestly,  my wife would see me to my grave if I used her
>>crock 
>>pot to melt this stuff lol lol


Yes.  It won't take hours, just minutes.  It helps to put a wood handle on
the can for ease of pouring.  I initially used the double boiler method
until an old-mirror maker turned me onto the following method:

1. Put pitch in its paper cardboard container inside a paper bag.

2. Beat it with a hammer to get it down to 1/2 inch chunks or so.

3. Put water in the can and drop one chunk into it and heat up.

4. As the pitch melts, sweep it out with a chopstick and let it cool a few
seconds, then roll it into a rod 1/8" in diameter. Let it cool in cold
water.

5. Pinch this slowly between my fingernails.  If it shatters right away,
it's too brittle and needs turpentine.  If it yields all the way thru, it's
too soft and needs some of the volatiles cooked out.  It should yield
halfway thru, then shatter as I pinch rapidly.

A Twyman tester is more scientific, but might be more than you want to
build for just one mirror.  There's not much to it, though.

6. Generally I find the pitch is fine as is.  If so, you're in luck.  Wrap
tape dam (I use masking tape) around the tool, and pour the chunks of pitch
and dust on top.  You want a layer between 3/16" and 3/8" deep.  Place it
on top of an old cookie sheet in the oven.  Set heat to 200 deg F. Watch
carefully -- it will melt in about 10 minutes.  (My wife loves the smell of
burgundy pitch, and, so far, hasn't complained much about the smell of the
other kind).

7. Meanwhile put the mirror in a container (I use tupperware) and add hot
water to warm the mirror.

8. Remove, quickly paint with a thick layer of cerium oxide + water.   Let
it cool until you can pull the tape off without pulling the pitch along
with the tape (when hot, the pitch will pull like taffy).   This usually
takes more than 10 minutes for me.  I am frequently not patient enough.

9. Pull the tape off and mate the mirror on top. Work the mirror around. 
Some pitch will squeeze out sideways -- you'll cut this off later.  You may
not make perfect contact everywhere -- don't worry, further pressing will
get you there.  If it doesn't, the pitch was too hard anyway.

=Matt



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