From: Jean-Daniel LEMOINE (jdlemoin@club-internet.fr)
Date: 11/11/02-09:27:34 AM Z
Some remarks about the real difficulty to make a Woodburytype, just to
complete the explanations given by Sandy:
1) The "WET or DRY thickness".
Nowhere in the technical books I have, the thickness of the resist is given.
Why? Because it can vary, as said by Sandy, for many reasons. At the end of
nineteen century, each person in charge of making the final printing on
definitive support had several hot gelatine containers with various pigment
percentage, just to accomodate this difference of mold depth. That's why
because it was difficult to control the thickness of the initial resist.
The carbon resist used to make the mold seems similar to the carbon print
resist but is significantly THICKER:
* let's assume a carbon print has a max thickness about .1 mm when DRY.
* We can admit that the Wooburytype has a similar thickness
* Therefore the original carbon print must be .1 mm thick when DRY, that is
to say must be 1 mm thick when WET (I suppose the case of a soft gelatin
capable to swell ten times in water)
Maybe these figures are not totally exact but the range of magnitude is
right: just to underline that the initial resist must be VERY THICK which is
not usual for the carbon print. This technics is rather in the phototypie
(collotype)domain.
Why a such thickness is necessary? Just to limit the effects of the flatness
of the various supports used (steel intermediate support and final paper
support), each flaw being exactly printed. Less thick the mould, more
pigmented the gelatine, more apparent the flaws.
To obtain this thickness, it is necessary to:
* put the dichromate directly in the hot gelatine bath (as for phototypie)
* determine the right quantity of pigment to control the right hardening
depth during exposure. Not easy. Requiring experiments.
* get this very thick gelatine layer (4mm when WET are recommanded in my
books!). Paper (or collodion) is not suitable as support, due to huge
curling problems. The solution I use is to replace paper by silk screen to
support this gelatine layer: able to symmetrically dry on the two faces,
this choice limits curling.
* dry successfully the layer and keep it in the adequate atmosphere.
* determine the right exposure time
* transfer on a perfectly flat and polished hard metal board and develop in
hot water.
* let the resist evenly drying. The complete drying time is very long and
variable (depending on the temperature and environmental humidity). During
this drying operation, complex dark reaction phenomenums begin to occur,
making very variable the sensitivity of the gelatine. So the initial resist
thickness can vary and therefore the mold depth. That is why it was (or is)
necessary to use several pigments ratio cantainers for the final printing.
2) After this preliminary operation, the 'molding'operation may be
considered from several points of view:
* If one wants to be in accordance with the Woodbury spirit, use lead and
hydraulic press to make the mold.
* If not, use a soft molding process as suggested in the mails: an adequate
silicone or epoxy compound will work well. Maybe could it be possible to do
this 'soft' molding operation when the resist is still WET, so limiting the
thickness necessary for the initial resist!
3) Once the mold made, the printing can take place under a low pressure
device but you will have to use a perfectly flat paper as an image support
because all flaws of flatness will be visible on the print.
My conclusion on this process
Due to a not perfect molding process and a not perfect printing, the
Woodburytype is less precise than the carbon process and dedicated only for
low cost (high) production purpose. So if one wants to make a woodburytype,
it is only to perpetuate an historical process: interesting! But if one
wants to be very faithfull to history, one has also to use the nineteen
century available materials which today is a challenge as far as the
perfecly flat materials (metal or paper) are concerned.
I agree with Sandy: for a limited edition, it is better and less uncertain
to use the classical carbon process; the 3D effect is only the result of a
big resist thickness + a low pigment ratio in the gelatine. Other advantage:
the process is not sensitive to the paper flaws.
About precision or imprecision of a Woodburytype, many causes can degrade
this precision:
* The operation under hydraulic press is very delicate, due also to the
problem of air bubbles likely to be trapped in the details of the image.
* During the final printing, it depends also on the time between
'thickening' and mold opening time. An other problem: the mold has to be
greased between two printings: the grease has a tendancy to fill the
'details' of the print, 'blurring' the print. Anyway, as written by Dick, it
is visible only under a magnifier. Maybe the epoxy molding process could
give better results than the historical process. Who knows?
For 5 years, I have had a small hydraulic press in my garage. My dream is to
be able to devote one year to experiment the Woodburytype process, but...
life is short and I have so many things to do before! I must admit that my
actual experience is very short: I just began to carefully study all my old
books and to make gelatine layer. Perhaps some errors!?
Sorry for this long mail: difficult for me "de faire court dans mon mauvais
anglais"!
Jean-Daniel
(Today, 11th november 1918, date of the end of First World War, a moment to
think to all people killed during this war, and specially to American
Soldiers, a lot of Sammies sleeping in battle field cemeteries in the north
of France.)
Jean-Daniel LEMOINE
2 allée des Pervenches
91570 BIEVRES
33 1 69 41 09 48
http://perso.wanadoo.fr/lemoine.jd/
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