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question on adding turpentine to pitch

Started by BABOafrica, 08/06/2012 07:47AM
Posted 08/06/2012 07:47AM Opening Post
I getting ready to make a pitch lap for a 12.5 inch mirror.

I have some pitch from a batch made for ATM use several years ago. The label says Gugulz (made in Switzerland) and looks like pitch alright. It's #73.

I read somewhere that one should add a bit of turpentine before heating.

Can I use "white spirit" paint thinner? (I have industrial quantities of that stuff lying around.)

Can I use mineral turpentine? (Dirt cheap and available.)

In Kenya (where I live) nobody sells wood turpentine.


In lumine tuo videbimus lumen.

8O Home-made 10” Dob / Home-made 4” refractor

EPs: Konig 32mm (1.25") / Zhumell WF 30mm (2") / Nagler 13mm T1 / Orion Sirius Plossls 25 & 10mm / Zhumell Plossl 9 mm / Meade MA 9mm
Posted 08/06/2012 01:52PM | Edited 08/06/2012 01:55PM #1
The purpose of adding Turpintine or other such solvent is to soften the pitch so that it somewhat *flows* under the pressure of your working the mirror against it. Too soft a resultant pitch lap is also not good, just as a too-hard of a lap could be. So, those mentioned solvents available to you should readily suffice for the purpose (the pertroleum-based versions were invented to be less expensive than wood-based Turp). But before actually thinning the warmed pitch *just because* you heard you *should*, I suggest you read comprehensive instructions per mirror & pitch lap making so that you have a full understanding of what you are producing & wanting to accomplish. And mind the heat source when using volitle solvents (Turpentine was also known as lamp oil & used as a less-costly substitute for whale oil before the days of electric lighting; petroleum-based solvents are more volitile).