dpb wrote:
On 2/2/2013 11:48 AM, dadiOH wrote:
RonB wrote:
I use a fair amount of wiping poly finish and have used pre-mixed
and my own 50/50 (poly/spirits) brew.
...

Adding thinner won't change the sheen. The dulling agent works
because it makes tiny little bumps that reflect the light
differently...same effect as sanding with very fine sand paper.

Well, the end effect is similar but that isn't the mechanism by which
flatting additives work--they do cause light reflection to be
different but not by causing surface roughness by by having
refractive surfaces on the particles themselves...

Which would mean they are exposed. Which means they roughen the surface.

The flatting powders with which I am familiar are talc and fumed silica.
The roughness created depends on how much of which. I used to make my own
mix for flatting lacquer using talc; I wanted a surface rough enough that it
would pick up pencil marks (I was retouching photographic prints). Add
enough talc and you get a *very* rough surface...maybe around #360 silicon
carbide or coarser. It isn't a hard surface, of course, and will scratch
white.

Also, I know that most flatting agents are sold in a paste form. Doesn't
change the fact that they are generally talc and/or fumed silica
("Cab-o-Sil") that have been mixed with whatever to make a paste. Used to
be one could go to a paint store and buy flatting powder by the ounce or
pound. No idea why that is no longer true but would guess that they can
sell it for much more as a paste. Obfuscation, IOW.

--

dadiOH
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