Home made 'polishing pitch'
Posted 28 June 2006 - 03:10 AM
Since it is not possible to find 'polishing pitch' in local market where I live, I want to try to make it. Currently, I'm about to mix and melt colophony, beeswax and turpentine to see if it would be possible to make a suitable mixture that will not deform easily yet conform the curve in my 8" f/6 mirror. The weight ratio of these will be 91/6/3 respectively.
Can someone give a better formula?
Posted 28 June 2006 - 03:48 AM
Posted 29 June 2006 - 12:33 PM
Posted 30 June 2006 - 02:00 AM
Posted 30 June 2006 - 06:24 AM
2 lb coal tar (melting point, 170 to 180 degrees F)
4 oz. Pine tar
1.5 oz. beeswax
2-3 cc. Venice turpentine
Melt the tar, add remaining ingredients in order listed, stir well after each addition.
I hope this formula helps to other Amateur Telescope Makers living in countries where commercial pitch is not available.
I'll try the formula and provide feedback about my findings.
Posted 30 June 2006 - 10:04 AM
Posted 03 July 2006 - 01:02 AM
During the weekend I've experimented with various proportions of the ingredients. It seems that the original formula provides a very soft pitch for summer (> 85 F)temperatures.
I've then decreased the amounts for pine tar, turpentine and beeswax in order to make it hard and it worked.
You can take a look at the photograph of the finished 6" lap @ http://tinyurl.com/obg7f (sorry web site is in Turkish w/o English translation yet)
Conclusions so far;
- If you can not buy pitch from the local market, then it is possible to make it,
- The working temperature is a VERY important criteria for pitch so the formulation has to be adjusted accordingly, especially for the hot weather,
- Coal tar is very difficult to work with. Colophane is easier but more brittle. Eventually, I'm sure that both can be used in pitch formula.