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Re: Etching copper type



I have been photoetching copper etching plates for 20 + years with ferric
chloride, also known as iron perchloride.  Industrial ferric chloride is
sold as a corosive liquid in 42 degree balume solution in five gallon units
from large chemical vendors. Some of the the printmakers supply houses sell
dry lumps to mix with water. They aren't worth the trouble.  The material
is hard to get into solution. I always use liquid technical grade which is
far cheaper than any reagent grade from a school lab supply. I mix it with
equal parts tap water which will give you about a 20% solution.  A 20%
solution will etch faster that a heavier concentration. I etch copper at
80-100 degrees F which will about .0002 of an inch per hour at 80 degrees,
if the solution kept hot and is a large enough bath.  Heat increases the
speed of the etch.

Dutch mordant will produce much finer etching which could be useful for
halftone work but is MUCH slower.  Any good printmaking book will give you
a recipe.  Roughly it is 88 parts water 10 parts Hydrochloric Acid and 2
parts potassium chlorate (45 ounces, 5 ounces, 1 once)  Mix it outside to
avoid the chlorine gas that forms.  Exposed it to the open air for 20
minutes and use with ventilation.

I would not use nitric acid for copper. Too slow and too much laterial
etching,

As for the image transfer a photetched image can be deep etched with two
traditional processes.  To protect the edges of your design from the
mordants lateral etching you can bank the edges with the dragons blood
process or by richly rolling the plate surface and exposed edges of the of
the design with ink and dusting it with rosinand fixing with heat.

Both processes are well documented in pre WWII photpengraving manuals.  Too
involved to detail here.

My considerable research and testing has made me conclude that the best
adaptation of old or current processes for your needs would be to not use
copper or acid or any dusting methods!

I would:

Tranfer the image with the new Safe photoetching emulsion films like Dupont
ImageOn and electroengrave the metal with a reverse plating process.  I
would use mild steel for line cuts.  It would hold up better than most
non-ferris metals and would be fine for detailed work. Electric engraving
was popular before Dow Chemical invented the oil/acid/water activated Dow
Etcher in the mind '50s. Electric etching creates the sloped edge as found
with metal type.  The pyramid structure is a natural part of the electrical
engraving process. When I finish my testing I will share more details......

Some of my research was conducted to make plates for foil stamping custom
hard hats! Mag plates would be pounded into mush half way through the run.

Michael Morin
Celtic Press-Buffalo NY


At 06:02 PM 2/25/98 +0000, you wrote:
>Has anyone any experience of etching copper for making type for hot foil
>printers?
>
>In the past I have used rubdown transfers on copper-clad board to produce
>printed circuit boards, etching with ferric chloride. I am wondering if
>this process used on a thicker copper plate or block would produce a deep
>enough cut with out causing an undercut too far under the raised letters.
>
>Any Ideas gratefully received before I start investing in R&D.
>
>Mark Rimmell
>temple@globalnet.co.uk
>---
>


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