Re: [ATM] Melting Pitch

[Mike Lockwood <melockwo@uiuc.edu>]

Richard,

Richard wrote:
> It's been many a decade since I melted pitch. In this safety
> conscious PC world, how do we melt it now?. The H&S (MSD) sheet
> says not to let e naked flame anywhere near it, yet I'm sure
> that's how I did it when I were a lad.

I use a $20 electric hot plate that I bought at Kmart.  It's got a 
temperature control with a wide range of adjustment.  I plug it in on 
my porch (outdoors) and melt the pitch there.

When I get an infrared thermometer, I will measure the temperature 
that I'm melting it at.  It takes about 30-60 minutes to fully melt a 
pot of it.

> One piece of information that I cannot find is the actual
> melting point of it. I'm using bitmumanous coal tar pitch called
> Gugolz 63 and 74. Is the Gugolz number equal to the melting
> point in degrees C by any chance?

It does not appear to be, but it's close.  The source of the info 
below (Meller Optics, Inc.) indicates that Gugolz is wood resin based, 
not coal tar based.  Is it possible there are different versions?

Anyway, here's some info from a document that I found on the web:

Gugolz        Melting Pt   Flash Pt   Burn Pt   Softening Pt
55-Very Soft   52°-55°C     246°C      278°C     63°-64°C
64-Soft        68°-72°C     229°C      262°C     65°-68°C
73-Medium      77°-80°C     219°C      254°C     71°-74°C
82-Hard        79°-82°C     210°C      246°C     75°-77°C
91-Very Hard   84°-87°C     213°C      252°C       78°C

For others who might wonder about pitch hardnesses, at 65-70F (sorry 
to mix units!), I like Gugolz 55 for figuring and Gugolz 64 is nice 
for polishing (removing pits).

Gugolz 73 is quite hard, and I like it for flats.  It is not easy to 
get a smooth parabola with Gugolz 73 unless the temperature in the 
workshop is quite a bit higher.

	Mike Lockwood

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