I have recently done a photogravure workshop with the people from the "Atelier Estrela Brasil Oriente" here in São Paulo. It's not my intention in anyway to provide a “complete guide” on photogravure here as you can easily check everything about this amazing 19th technic over the web, particularly here www.photogravure.com. This is just my own way of documenting and recording what I did at this great workshop at Sesc Pompéia.
First of all you need a copper plate slightly bigger the size you want your image, they're not cheap and you'll spend a lot of time polishing in order to make it “shine like a mirror”, so try getting one with less damaging or scratches as possible or you'll might have to spend a good hour polishing... here's my “before and after”.
After cleaning, the plate is inserted in a box containing rosin for 2 minutes. Prior to that, the box must have a sort of mechanism to agitate the rosin inside, making the grains float for a few seconds. The time you wait the grains to sediment in the box is what will define the size of the rosin grains needed for the process (in my case 20 seconds).
After 2 minutes, the plate is removed from the box and then taken straight to the heating area to be fixed.
Once it's fixed, the plate is ready to receive the gelatine previously made light-sensitive with a 3.5% solution of potassium bichromate at 15º and dried for an hour at room temperature/50% humidity, the image will be exposed under the UV light.
Making a contact print with negative and the sensitized gelatine
So I had my digital positive in acetate adjusted in PS in order to get the most in terms of tonal range. I then made the contact under the UV light so I could get the image recorded on my gelatine. It's always good to remember that you start with a positive image because you're making the negative onto the copper plate.
Receiving 2.30'' of UV light.
After exposing it, you'll need to place the gelatine onto the plate with the desired position, you should do this by immersing first the plate in a tray with water at 15º, and then the gelatine. Start guiding in the position wanted gently with your hands until the sheet adheres to the plate, this process should take five minutes. Use a squeegee to get rid off the water excess and finish by pressing with a cloth making sure no bubbles has been created. Leave again to dry for 20 minutes with a piece of glass on top.
To remove the paper base you should do this by giving several baths of water at different temperatures, starting at 32º and then gradually move to a hotter mix (36º, 39º, 42º) and with running water at 44º. You should keep it until no signs of dichromate can be seen in the water, that means the gelatine is getting soft again and the paper base will come off, the whole process should take about 7-10 minutes. Once the paper base comes off you will have to decrease the water temperature slowly until reaches 15º.
What happens from now is that the gelatine that got exposed under the UV light is hardened onto the plate, what didn't get exposed will be washed away during the acid bath. Before that you need to protect the plate borders and back with a good masking tape and contact paper. The reason you do that is that you can get a nice border on your final print.
Leave it to dry for about eight hours so the gelatine can settle again to its normal. The plate then is finally ready to go to the sequence of acid baths.
The acid used is Ferric Chloride and there are several baths that can be use during this process in order to achieve better grey tones. Each bottle of this has a different thickness of acid, which is measured in Baumer (Bé) . So we start with deep blacks in 48º and 45º "Bé", we then move to 43º, 41º and 39º Bé for the greys and mid tones and lastly (depending upon your image), 37º Bé for the highlights. Something I'd suggest is to have a copy of the image you're recording next to you, in that way you can check the progress on your plate and make the decison accordingly.
The numbers below shows the approximately time spent in each bath, it obviously depends on the image you have (highlights or deep shadows). You'll see the image appearing on the plate as the acid starts to work, which is a good way of deciding the amount of time you will spend in each bath.
- 48º / 1 minute 30 seconds
- 45º / 6 minutes
- 43º / 6 minutes
- 41º / 5 minutes
- 39º / 6 minutes 30 seconds
- 37º / 4 minutes 50 seconds
Once the plate is recorded is time to get the whole masking tape with alcohol and finishing with salt and vinegar to degrease the plate.
With the recorded plate dried, is time to put some printing ink on and do a test.
Clean the excess of ink with a soft cloth and you'll start seeing the image you'll get on the paper...
Put a slightly wet paper on the top of the plate (this paper should be left in the sink with warm water for at least half an hour) and pass through the machine...