Source for pitch

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Does anyone know a good source for pitch?

The only one I know is Galvoptics, but they are not cheap. 450g of 'best pitch' is £12.10, 450g of 'special pitch' is £16.74. I bought some of the best pitch, which was OK but rather hard. I ended up putting in 3 teaspoons of Linseed oil to soften it. If I buy from them again I will probably get the 'special pitch' just to see what the difference is. When I rang them I could not get an explanation of the difference . I also bought my 14 inch plate glass mirror blank from them, which seems good. I am just starting grinding it. I picked the mirror and pitch up, which was interesting, they are quite a small operation, I imagined a huge factory!

I could make a sub-diameter pitch lap, in which case I may have enough pitch. But I think I would prefer to make a full sized one (and possibly a sub-diameter one as well-I think having 2 different sized laps would help with figuring).

Given the price I do have fantasies of wandering round Epping Forest near where I live looking for Pine trees and figuring out how to get the pine sap out, which I think is what pitch is made of! However, this is probably not realistic!

Next time I buy some pitch I will buy quite a lot, as I have got the mirror making bug and want to have enough for future projects. 

David