Copper photogravure

Lars Mellberg shows us how he and his students work with the copper photogravure process.

Writer / Lasse Mellberg

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Always be careful when handling chemicals. Read the health and safety instructions.

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

We use Efke Op 12 lithfilm. 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 enlarger if you want it to come out the right way in the print. I am working with the JemseBy hybrid metod and see big possibilities to adapting it to the gravureprocess.

The copper 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 removed 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 grease 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 dangerous 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.

Pigment paper

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

For sensitising use 3% potassium dichromate solution.

Take care, it is dangerous!!! Wear dust mask and rubber gloves.

We dissolve 30 gram potassium dichromate in 1 litre of destilled water. It 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 process 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.

Finally we put the pigment paper portioned up in aluminiumfolie and store them in the refrigerator. If you freeze it will last for years.

Dusting and 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 dustmask because the dust is hazardous.

Rosin
It dissolves in alcohol, so you have to dust on to the dried, exposed and developed 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 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:

Peter Ragnarsson, Intermezzo Grafik, Planiavägen 28, Nacka
Telephone: 0046 08 716 9673

The screen is exposed 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 different 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.

For 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 alcohol 99,5 %.

The copper photogravure process

1Put the copperplate in a tray with transfersolution, 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.

2I put the exposed pigmentpaper in the tray with the transfersolution with the gelatineside 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 gelatine has relaxed and flattened out, I remove the copperplate and let the transfersolution 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.

3Put 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. Agitate the tray continuously, and change water until it is clear. When you can see the relief of the image on the plate, the development is ready. I cool down the plate using cold tap water.

4Place 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 minutes I take the plate up and pour 99,5% alcohol over it.

5Drying. 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.

6I 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

Ferric Chloride Etching Bath
45 Baumé, the highest saturated solution and the weakest bath
43 Baumé
41 Baumé
39 Baumé
37 Baumé ,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. Oh yeah, we use a densitometer for the positives but the gelatine is not a dead material it has 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.

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

Lars Mellberg lives in Sweden on a little island in Lake Mälaren where he works as a teacher and gives courses in alternative processes.