I have never coated anything with a glass rod but during my working
life I was closely concerned with putting a fine coating of PVA adhesive
onto smooth matt photographic base card.
We did, of course use a machine for production, but when tests and
experiments were needed I coated by hand using a Meyer bar.
A Meyer bar is a stainless steel rod that has been tightly wound with
stainless steel wire. It is used in the same way as a glass rod in that
a pool of whatever it is you are coating is pushed along and spread by
the bar.
I guess that with a glass rod you have to be careful to exert even
pressure and run it at a constant speed. And even then I cannot imagine
that it is easy to maintain consistency from one coating to the next.
With a Meyer bar it's easy. You just press as hard as you like as it is
the space between the turns of wire that determines the coating
thickness - it is more or less independent of pressure or speed.
The deposit you leave behind is proportional the diameter of the wire
wound on the bar and the thickness of the coat when dry also depends on
the solid content of the coating liquid.
The company who makes the bars does it to each customer's requirements
so that you can have a bar that will deliver the precise coating you
need, time after time.
Please forgive me if I have been telling most of you what you aleady
know but I thought that, since I had heard glass rods mentioned a couple
of times, I would say something about my experience in the field of hand
coating.
For anyone who is interested, the company in England making Meyer bars
is:
R K Print Coat Limited, Litlington, Royston, Cambs. SG8 0QZ
Telephone: +44 1763 852 187 Fax: +44 1763 852 502
Regards,
Dennis Atherton