It is my impression that after almost 20 years of answering a help line
that impurities from the chemicals used in the coating solution leaves
comet trails. This is due to the particle being dragged by the brush or
coating rod.
Potassium chloroplatinite solutions are often prone to "throwing" some
metal. It's the nature of the beast so to speak. We've had it happen to
some of ours, though we've really gotten better at making it over the years
and we've seen it happen to material from all the other major
manufacturers. (Yes we've frequently gotten calls on our Helpline from
folks who are having trouble with chemistry from other sources. And let me
assure you the big guys have had some really spectacular goofs. I had a
call from someone who had over a quarter inch of metal in the bottom of a
100 ml bottle he had just mixed up, and this was from the major industrial
supplier of platinum salts.)
There are basically two kinds of particles that can occur in the platinum
salts. One is the pure metal itself "kicking" out. This will be observed as
black powder in the bottom, or maybe just a few tiny particles. Observed
under a microscope these are puffy and cinder like, full of holes. There
are actually a lot lighter than they appear. If sucked up and coated, they
will leave observable black streaks on the paper before development.
The second is crystals of the potassium chloroplatinite itself. My 1954
Handbook of Chemistry and Physics gives the solubility specifications on
potassium chloroplatinite is approximatly 1 gram per 100 ml of water at 16
degree C. to a little over 5 gm per 100 ml at 100 Deg C. It is interesting
that we dissolve 20 grams in 100 ml as the standard mix used in platinum
printing! Either these figures are way off, or, and this is a guess, the
testers were using a super pure version and that is less suluble. The point
however is that at the concentration normall used in pt printing, it is
likely that some "salting out" will occur.
If these crystals were to get sucked up and coated, they to would likely
leave comet trails, but less visible than the metal particle trails. When
developed the extra concentration would darken and be more visible. A
third possiblity would be the presence of potassium choloroplatinate, which
is a mostly insoluble yellow powder -- actually K2PtCl6, and was at one
time used as a glazing compound for ceramics back in the days when folks
were trying to find a use for platinum. K2PtCl6 does not leave black marks,
spots or do anything spectacular to the image. Some of the older texts use
the "ate" and "ite" endings indescriminately, and occassionaly we will get
a call from folks who have bought the yellow powder by mistake.
Of course if there were iron particles floating about they could also cause
problems but this is a highly unlikely occurance. Drop a couple of iron
filings into your potassium chloroplatinite and it will be immediately
dissolved by the potasium chloroplatite or the palladium solution. Actually
not a true "dissolving" but a double replacement, but for all practivle
purposes, we cvan call it dissolving.
Of course this is not the same as dropping the tiny iron particles on the
paper. And here we are talking teeny eensy weeny itty bitty particles.
Outside contamination of iron (or any ferrous -- nickel or cobalt too)
particles is perhaps a bigger problem than previously thought. In the
course of 20 years we have traced several iron particle contaminations to
hair dryers self destruction where the fan was scraping against the metal
frame or bearings etc and grinding up metal and spewing it all over the
place. We had a case of rusty pipes above the coating area that shook when
the water "hammered" when turned on, (then the person took steel wool to
the pipes and had a coating room full of metal particles!) Then of course
the steel rule and cutting blade routine on numerous occasions.
A nice big magnet has shown to help in some cases but remember that much of
the ferrous metal world is non-magnetic, many stainless steels are
non-magnetic and can cause problems in printing as well.
Over the years we have learned that we will be on the firing line. The
tendency of most folks when they run into trouble is to blame the
chemistry. "I haven't changed a thing, Everthing is identical...." a
Bostick & Sullivan
PO Box 16639, Santa Fe
NM 87506
505-474-0890 FAX 505-474-2857
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