[ATM] Sharpie test: a little help?

[Ross Sackett <rsackett00@yahoo.com>]

Hi all,

The last time I worked on a mirror, Nixon was in the
White House and I was sweating the draft lottery,
hoping for a high number.  Since then, I have let
others make my mirrors.

But now, in the mid-afternoon of my life, I have
decided to get back to the barrel.  My 6" went through
#80 carbo in a day, with the sag right where I wanted
it, and today I got through #120. LOTS easier than I
remember, way back when. 

Here's my question: I've read several different
descriptions of the Sharpie test for good contact, and
I've tried it a couple different ways (1 wet of 1/3
COC strokes, a few very short strokes, a wet of little
half-inch circles, use fine Al-Ox rather than the
current grit, etc.).  The results seem to vary
depending on how I do it.  

In general, I seem to have good contact across most of
the face of the mirror, until I get to the "overhang
zone" on the edge: some ways of doing it the lines on
the edge stay rather dark, and other ways they get
ground entirely away while most of the face is still
ghosting out.  

During a normal grinding wet I seem to have good
contact, so I am pretty confident I am doing ok (at
least for #120 carbo), but I am bothered by the
inconsistency around the edges.

What am I doing wrong?  Opinions about the RIGHT way
to do the Sharpie test?  Best stroke?  Should I grind
a little MOT then TOT, or shouldn't that matter?

Thus is bugging me because the reason I gave up mirror
making before was a nasty big central bubble that just
didn't want to grind out; now I think I know how to
handle it, but I would much rather not get into that
situation again.

Ross


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