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Home made 'polishing pitch'

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#1 curiosis

curiosis

    Sputnik

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Posted 28 June 2006 - 03:10 AM

Greetings,
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?

#2 Stefan Rostyne

Stefan Rostyne

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Posted 28 June 2006 - 03:48 AM

You should also try a mix without beeswax. I experienced it not to mix very well with colophony. I also made a successfull pith with 'carbopith', an industrial component from a local asphalt producing company. It was very hard stuff, but it was easily softened with turpentine or white spirit. Didn't use beeswax in that mix either.

#3 greenglass

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Posted 29 June 2006 - 12:33 PM

I just boiled pine gum in a can from blobs on tree trunks, Ew there was a worm living in that stuff.

#4 Chriske

Chriske

    Kijkerbouw Urania

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Posted 30 June 2006 - 02:00 AM

While it's swimming in that stuff give him some soap so it can open it's eyes again to see what your up to... :lol:

#5 curiosis

curiosis

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Posted 30 June 2006 - 06:24 AM

I've just received some valuable information from an expert. The receipt is from a book, Procedures in Applied Optics, by John Strong (1989).

He suggests:
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.
Regards

Curiosis

#6 Stefan Rostyne

Stefan Rostyne

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Posted 30 June 2006 - 10:04 AM

Please keep us informed on your results. Take care with carbon tar, this stuff is highly carcinogene!

#7 curiosis

curiosis

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Posted 03 July 2006 - 01:02 AM

Greetings,

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.

Regards,

Curiosis


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