>> ...tropical pitch hasn't worked on the first two tries
>What in particular didn't work ? Did it get dissolved by alkaline
>slurries ?
This stuff (tropical pitch) is unusuall in that when its stone cold, it's hard as a rock, but as soon as the littlest amount of heat builds up, it starts to flow, fast. First attempt was way to soft, when at room temp., you could press your thumb nail way in. Silicon is much harder than glass, and polishes easily when heat and alkalinity are present. This is a demanding enviornment for pitch to operate, as the particles in the collodial silica are in the order of 50 nanometers in size, and mechanical aspects of polishing do not contribute much, and polishing is achieved by the 'melting' of the silicon by chemical means with heat from friction of the polishing tool surface. Urathane pads can stand it. Pitch doesn't. Success has been achieved by 'charging' the surface with ziconium oxide, which produces a crust that can resist the pH but still will flow, and produce test, but sleeks are usually present. I'm trying to find that perfect combination that will allow the use of heat (read speed and pressure) and pH to allow the chemical removal...this is a industry problem, which is why I can get away with doing this in the shop, as results will benifit general production as well (besides the fact I run the shop.....) Anyway... attempt 2 was a little harder, but still started sticking whith anything approaching the rpm (50 -60), and psi ( aprox 25 lbs) that I'd like to use on the 5" mirror I'm working on. Attempt 3 is MUCH harder, and I plan to take it a little easy on the speed and pressure....we'll see.....
Bill Marriott Forest Knolls, Ca. USA btk@ix.netcom.com