Re: ATM 10" help - TDE?

["Ken Hunter" <kb7h@onemain.com>]

----- Original Message -----
From: "Tyrone Steele" <atm@pivotmusic.com>

> I have no idea what you're talking about.
> If you mean the sharpie test, yes that was done many times.

The SHARPIE test was not designed and DOES NOT tell you
if the mirror's surface is properly ground out to the edge. It merely
tells you that the surface is spherical (or not). There can still be
many larger sized pits anywhere on the mirror and the sharpie test
will pass if the glass is spherical. It's up to you to get a
consistant
grind over the surface then apply the SHARPIE test before deciding
to move to the next grit size.

Perhaps you were not applying the SHARPIE test correctly or were
unclear on it's purpose.

The mirror is marked on many axis with the SHARPIE marker,
A FEW, SHORT strokes are made and then the mirror is examined
to see where the contact between the mirror and tool occur. If the
SHARPIE lines are evenly ground, the mirror and tool MUST be
spherical and if the pits are uniform at the same time, move to the
next grit.

The "red out" test is described in the ATM series of books...
You basically hold the mirror or position yourself to see the
reflection
of a light bulb at a grazing angle off the surface of the mirror. By
raising
or lowering your viewing position you can see if the reflection
changes
color and determine the quality of the grind.

I'm not familiar with a "blind" test by that name, perhaps Richard can
elaborate on it or maybe it was an attempt for us to do a little
exercise
in Internet searches?

Ken Hunter