Jason -
This is my experience, so take it with a grain of NaCl:
I learned on pitch. Red pitch, not black. I avoid lead like it was
poison. It may have the most fabulous properties for repuosse, but as
an environmental engineer I can not justify its use. The sandbag may
work great but I do not have personal experience with it.
Here is the text from a post in February 2008:
"Red pitch and a bowl"
http://www.ganoksin.com/orchid/archive/200802/msg00869.htm
Wrap pitch in a sheet of newsprint, and wrap again in an old towel.
Take a mallet or hammer (not a good one!) and smack the heck out of
it. Check periodically for size of the resulting pieces; take out
those that are 1-1/2" overall or less. When done, set the pitch aside
in a sealed container - I use an old coffee can.
Though a purist would fill the bowl with pitch, I elected to fill
2/3 of the bowl with plaster of paris. If you do this, wait several
days for it to completely dry! It takes time, but saves on pitch.
When you are ready to put pitch in bowl, turn the oven on to 300
degrees F.
Make sure you have SPOUSAL UNIT APPROVAL before this next step!
Put some, but not all, pitch in the bowl…use less than you think
you will need. Better to build up slowly than to have a spill in the
oven! Your aim is to fill the bowl to within 1/8" of the rim. You
will find as the pitchgets closer to the top that the finer chunks
are better than the bigger chunks.
Check about every 10 minutes. Your oven may run hotter or coooler
than mine - adjust accordingly. You definitely don’t want the pitch
to be smoking! Some bubbling will occur, but it should not look like
it’s boiling.
When you have the pitch to the level you want, remove the bowl
carefully to a heat-resistant, flat surface. I would not leave it in
the oven to cool. Give it plenty of time before you use it! A hot
pitch bowl looks just like a cold pitch bowl.
Before you use your first time (I’m assuming you are going to be
chasing & repousse), gather these things:
chapstick
old rags
denatured alcohol (not isopropyl)
wooden paint stirrer
jar of water for the paint stirrer
heat gun
old needle nose pliers
the chapstick is for coating the back of your metal before putting
it in warm pitch. If you don’t do it, a lot of pitch will come up
with the metal when you are ready to remove it.
Rags & alcohol for cleaning off the metal. When you get really good,
you won’t pull any pitch away with the metal when you release it. But
until then, you will need to be prepared to clean up.
Use the heat gun to melt the pitch slightly. don’t be in a hurry -
you don’t want the pitch to smoke or bubble. When putting the metal
in the pitch, use the heat gun on the pitch. When it’s soft enough,
just push the metal down into the pitch, and use the paint stirrer to
push the edges of the pitchover the edges of the metal. Wait until
the pitch is as hard as a cold tootsie roll before chasing or
repousse.
ALWAYS assume the pitch is hot enough to burn your fingers.
To remove the metal, heat the metal, not the pitch with the heat
gun. Grab a corner of the metal with the needle nose pliers and pull
’up’ as much as possible. Don’t drag the metal through the pitch, or
too much will stick.
To flatten the pitch, prepare the surface, scoop up pitch to put on
metal for chasing support, use the paint stirrer. It must be kept
wet! If it dries out (& that happens faster than you’d think), then
the pitch will stick to it & make a mess. I’ll bet you were wondering
where that jar of water comes into play - that’s where the paint
stirrer lives when waiting to be used. Dip it frequently when moving
pitch around.
I know there’s stuff I left out, but in the interest of sending it
in a timely manner, I’ll quit now. Good luck with whatever your
project is.