Re: Re:Photogravure

biskops@algonet.se
Sun, 21 Apr 1996 11:48:12 +0100

PHOTOGRAVURE

I have been working with photogravure since 1987. Since 1992 I have
conducted courses at Biskops Arn Folkhighschool in Sweden. The courses are
about 17 weeks. They have 10 - 12 students in different ages. This has
given possibilities to explore the teqnique and as always you learn much
when you work with it. The workshop is built for the photogravure process
it is not big but lovely to work in. I am not saying that our teqnique is
the best but it works and gives good results. I think it's is good if you
have some experience from the process or have read the book" Keepers of
light" to understand all the terms. I know there is a big interest for
photogravure but it is practices by few , I wish there where more people
working with it, because it is a fantastic process. Our teqnique is as
follows:

POSITIVE

I use Arista halftone supreme film which I buy from Freestyle ,
California. Using it with selectol - soft or similar developer.
The density of the positive could be between 0.20 - 2.60 depending on the
aquatint or screen we are using. I know it seems very high but it works.
You put the negative emulsion upwards in the enlar=1Fger if you want it
to come out the right way in the print .

THE PLATE

We use copper. I try to buy as scratchfree copper as possible, I pay extra
to get one side covered with plastic.
The thickness of the copper is 0.80 millimetres but it doesn't matter if
you use 1 mm or thicker.

After removing the plastic adhesive on the plate , wipe it of with alcohol.
Look for scratches. Everything that you can feel with a nail has to be
polished or burnished with a burnisher.
We use polish like Brasso or similar.

We use whiting dissolved with water mixed up to a liquid paste , apply
it with a brush and use a piece of rag to polish with. When the paste is
remo=1Fved you take the paste again and apply a layer on the plate with a
brush. If you can't coat the copper with it, where is it too much gre=1Fas=
e
on the plate, so redo step one again. When you have coated the plate
with the paste , use some kind of burner and heat the plate until the
water has evaporated from the whiting . You can see it very well when
the plate is dry.

If you do as above , you get many advantages - you don't need to use
dang=1Ferous chemicals and you get a shiny greasefree copperplate. You can
leave the dried chalk on the plate until you are ready to lay the
aquatint or use the screen.

PIGMENTPAPER

We use Autotype G 25 . You buy it in rolls and it is important to store
them in a place between 18 - 22 degrees ( Celsius ) and a humidity between
55 - 65 %. We always practice the same methods when working with the
pigment paper.
The room has to have a humidity of at least 65%. Use a humidifier to
achieve this .Use cotton gloves and a clean working area. Roll out a piece
of paper at let it settle down for a few minutes to absorb the humidity
and relax.
Cut the paper to the size you want, it is always good to have a bigger
paper than you need.

SENSITISING

=46or sensitising use 3% potassium dichromate solution. Take care , it is
dangerous !! Wear dust mask and rubber gloves.
We dissolve 30 gram po=1Ftassium dichromate in 1 litre of destilled water. I=
t
is enough for 1 square meter pigmentpaper. The sensitising temperature is
between 12 - 16 degrees Celsius. The time is 3 minutes. Try always to do
this in the same way because this pro=1Fcess have so many variables.
Put the paper face up in the tray and agitate carefully , use a soft brush
or a feather to remove air bubbles.

Drain the paper and then lay the gelatinside down on a sheet of stiff
,clean plexiglas.
With a squeegee remove the excess solution from the back of the paper.
Clean the sheets of plexiglas with alcohol, just before laying over the
pigmentpaper. Depending on the roomtemperature the drying time of the
pigmentpaper can range between 3 - 8 hours, make sure humidity stays the
same.

The best thing is to do everything in one room.
The sensitising is handled in a humidity of 70 % .It could be higher.

Peel off the pigmentpapers carefully, it should come of easy.
=46inally we put the pigment paper portioned up in aluminiumfolie and store
them in the refrigerator. If you freeze it will last for years.

DUSTING & SCREENS

I am familiar with four different teqnicues to acquire a random dot
pattern on the plates that will achieve the halftones for this process.

Dustbox

To build your own box, look in the book "Keepers of Light "or a similar
book. about printmaking techniques. Remove the whiting from the
copperplate with a dry cloth. Place the plate on a sheet of white paper,
whirl up the dust let it settle and use the white piece of paper as a
reference to determine the density of the dust. The use of a magnifier
will greatly enhance the wiewing. Use a dust -mask because the dust is
hazardous.

Rosin

It dissolves in alcohol ,so you have to dust on to the dried, exposed and
deve=1Floped gelatine. The plate needs to dry for about 6 hours. It is
important to get a rich, fine coverage on the resist . Traditionally a
coverage of 30 - 50 % is recommended. We try to get up to 90 %, but it
depends on your etching technique.
The rosin gives a " big " corona round the etched dot.
I have seen beautiful results made by Jon Godman and Deli Saciloto. I=B4 am
deeply impressed of theirs knowledge in photogravure.

After you have had the plate lying in the dustbox use a burner to melt the
rosin. You have to be very careful because the rosin have a tendency to
melt together when heated .

Asphalthum

Asphalthum gives a fine coverage of the plate. After you have got the
dustclouds going in the box , wait for about 2 minutes to let the coarser
particles fall down. Leave the plates in the box for 15 - 20 minutes.
Repeat it if you don't get the result you want. Then burn the asphalthum
at higher temperature .You have to practice. It is easy to get oxidation
on the plate, you can remove them later in the process.

Xeroxpowder

Xeroxpowder could be used instead of asphalthum. It is much finer and gives
a very high resolution. It melts at lower temperature and have some
advantages, for example you don't need to use strong solvents to remove the
powder from the etched plate.
You just move the burner over the plate and the powder disappears. I have a
big dustbox for this and it is grounded to avoid electrostatic
explosions.
I get the powder from the recyclable boxes used to collect used up powder
from the copy machine in our library.

Screens

We have made our own screens ,they have a coverage of 87 % and a density
of 0,70 or 0, 80. They are going to be produced by a Swedish
reprospecialist for selling. The price for one screen of 40 X 50 cm is
around =A7 100.

Peter Ragnarsson
Intermezzo Grafik
Planiav=E4gen 28
-S-13134 Nacka
SWEDEN
# 011 46 08 716 9673
The screen is ex=1Fposed directly on the pigmentpaper before the positive
exposure .

EXPOSURE AND TRANSFER

I have the fortune to have a Theimerbox with vacuum and computer
controlled UV - light meter. So when the lamp gets older ,the clock moves
slower. My lightsource is metalhalogen. But the process works with a
lot of dif=1Fferent kinds of lightsources, for example sunlamps.

It is important to have good contact between the positive and the pigment
paper in the vacumframe. Mask the borders of the image with lithotape. The
emulsion side of the film , should not be taped.

=46or the transfer I use a water-alcohol-solution of 25 %:
Boiled destilled water. It is boiled 10 minutes and then put a side for
cooling down. The alcohol I use is Industrial al=1Fcohol 99,5 %.

1. Put the copperplate in a tray with trans=1Ffersolution ,after removing
any oxidation in a tray of salt, vinegar and water . Make sure that the
plate is rinsed thoroughly . The pigmentpaper has became acclimated
itself to the humidity of the room previously by leaving it in the foil
package an hour before use.
Cut the pigmentpaper in a size of the outside border of the positive
that has the lithotape.

The exposuretime depends on your lightsource ,and you have to do some
tests, The etching should start within four minutes in the most
saturated ethingsolution.

If I use a screen, I do the screenexposure first. Our usual time is 1
minute for the screen and 3 - 4 minutes for the positive.

2. I put the exposed pigmentpaper in the tray with the transfersolution
with the gela=1Ftineside down. After around 30 seconds it begins to
flattening out. Then I turn it face up in the tray and use a fine brush
to remove the airbubbles. After the gela=1Ftine has relaxed and flattened
out ,I remove the copperplate and let the transferso=1Flution drain off.
Then I put the plate on a newspaper and use a squeegee to adhere the
pigmentpaper in absolute contact with the copperplate.
Dry the backing with a piece of cotton rag or paper , and leave it to
rest for 10 minutes.
During this time , I filter the solutions so they can be reused later .

3. Put the plate in the tray containing 99 % alcohol let it sit there until
the paper is completely saturated about a minute. Develop in a tray with
hot tap water. As long you could keep your finger in the water it is okay.
Agi=1Ftate the tray continuously, and change water until it is clear. Then
you can see the relief of the image on the plate. Then the development is
ready. I cool down the plate using cold tap water.

4. Place the plate in a empty tray and pour an 50% Alcohol solution over
the plate, I make this solution in the same way as the 25% solution. After
2 minutes with continuos soft agitating I take a brush and brush
carefully over the gelatine to remove bubbles and left over gelatine
after 4 mi=1Fnutes I take the plate up and pour 99,5% alcohol over it.

5. I use an old record player with the speed of 78 rpm for drying, I place
the plate on the turntable and let it spin for 5 minutes and after that
I use a hairdryer for drying up the plate while it is still spinning.
After about 10 minutes I look at the plate against the light and it
should have the same colour over the entire surface. If it has darker
areas it is not dried enough .

6. I Use packingtape or maskingtape to cover the edges around the
image , then I leave it to rest 4 hours. After drying I cover the back of
the plate with tape.

ETCHING

=46erric Chloride Etching Bath

45 Baum=E9 ,the highest saturated solution and the weakest bath
43 Baum=E9
41 Baum=E9
39 Baum=E9
37 Baum=E9 ,the lowest saturated solution and the strongest bath.

I always buy Ferric chloride as a liquid solution. I have had to much
problem with dissolving from cakes. I prepare the different strengths by
adding destilled water.
The etching is the most difficult part of the process and my experience is
that every image is unique. O yeah we use a densitometer for the positives
but the gelatine is not a dead material it have its own life.
It is not necessary to use all the bath, often it is enough with just the
3 - 4 bath. Lately the we have been using two bath.

Then etching is finished I rinse the plate in hot water and thereby
removing the gelatine. Then the plate is prepared for printing.

Good luck .

Lasse Mellberg
biskops@algonet.se