The Oil Pigment Process
by Ed Buffaloe
Oil pigment printing, sometimes referred to as the Rawlins oil process, is the predecessor of bromoil. Originally conceived and practiced by Alphonse Louis Poitevin in the mid-1850’s, using a roller to spread the ink, G.E.H. Rawlins introduced the use of a brush for selective application of ink in 1904. The oil pigment process works on the same principle as lithographic printing--oil and water don’t mix. Essentially, a gelatin-sized paper is coated with a bichromate solution, dried, and exposed through a negative. The gelatine is selectively hardened where the light hits the paper. After the paper is washed and dried, it is soaked in water. The gelatine swells, except in those areas where it has become hardened. Thick oil-based printing ink is applied to the paper and sticks to the areas with hardened gelatine, but the water-swollen areas of the paper repel the ink.
The paper with selectively hardened gelatine is known as a matrix. The primary difference between an oil print and a bromoil is that the oil print requires an enlarged negative, whereas the bromoil starts with an enlarged print. In the bromoil process, the enlarged print is bleached with a copper sulfate/dichromate solution and the gelatine is hardened selectively wherever the silver was present. It was Howard Farmer (of Farmer’s Reducer fame) who discovered, in 1889, that dichromate will selectively harden the gelatin of a silver print when the silver is reduced. Then, in 1907, E.J. Wall wrote a brief article suggesting that this property of dichromate might be used to make oil prints from bromide prints, and later that same year C. Welborne Piper published details of the process. In my admittedly limited experience, it is easier for a beginner to make an oil print matrix than it is to make a good bromoil matrix. That doesn’t mean that the oil process is easy--I’ve only had about a 10% success rate, even after considerable experience with the process.
I first encountered the oil pigment process through Ernie Theisen’s article A Method For Making Oil Pigment Prints. Since I had been making enlarged negatives for the Vandyke and salt paper processes, I realized I already had everything I needed to make oil pigment prints. I achieved success very quickly by following Ernie’s instructions carefully. After reading Ernie’s article, I began to do some research and discovered other useful sources of information on the process.
Preparing the Paper
Ernie Theisen recommends fixing out regular photographic paper, and that is exactly what I did. I had several boxes of very old Agfa Brovira, Agfa Insignia, and Kodak Azo. These all worked very well, though I prefer the Brovira over the Insignia because it has a white rather than a buff paper base. The Azo I used was the old double weight, and it worked quite well, but it was all 8x10 and I prefer to work with 11x14. Theisen says he has tried Agfa and Forte papers and they work fine, but he hasn’t been able to get the process to work with RC papers.
The procedure is very simple: agitate the unexposed paper for 3 minutes each in two trays of film-strength rapid fix, wash for 5 minutes, agitate for 3 minutes in a tray of Kodak Hypo Clearing Agent, and wash for an additional 20 to 40 minutes. The final wash time may vary depending on your local water quality.
You can also coat your own paper with gelatin sizing, and I found several sets of instructions that vary in details but not essentials. John Barnier recommends using a brush or rod to coat 250 bloom gelatin onto sturdy paper. He says you shouldn’t need to harden the gelatin if you use 250 bloom or higher, but if necessary he recommends a 2 minute soak in a 0.5% solution of alum, followed by a brief rinse in plain water. He suggests three coats with hot gelatin, and the paper should be dried thoroughly between each coat. When using gelatine size, it is generally recommended to hang the paper by alternate corners with each coat to assure even coating. The only problem I have encountered with sizing one side of a piece of paper is that it curls badly--this problem is obviated by coating both sides, but coating both sides is easier if you simply submerse the paper in the gelatine mixture. If the submersion method is used, you must be careful to either brush out any bubbles in the gelatine, or carefully draw the paper over the lip of the tray so that the bubbles are removed.
Klaus Pollmeier recommends using a 15% solution of gelatin with a small amount of dextrin (potato starch), which he says makes the oil adhere better. The ratio of gelatin to dextrin should be 10:1. He also recommends adding small quantities of chrome alum and acetic acid. See the link below for details.
Terry King recommends three coats of gelatine, the first being 5% with about 15 grams of chrome alum added per liter. He advises that the second and third coats should be 7% gelatin with no hardener.
I sized some Fabriano Uno cold pressed paper, using Terry King’s instructions, but I find the paper to be too rough. I thought the gelatine would smooth out the paper texture, but it didn’t. Next time I am going to try a hot pressed paper. I found that the process is lengthy and requires a lot of gelatine. I recommend buying gelatin in 20 pound batches, if you plan to do much of your own sizing.
Sensitizing the Paper
I simply followed Ernie Theisen’s advice on sensitizer. He says take a saturated solution of ammonium dichromate (approximately a 25% solution) and mix it with an equal amount of distilled water (so you end up with about a 12.5% solution). This worked for me. Terry King recommends a 2% solution of ammonium dichromate or a 3% solution of potassium dichromate--it may be that hand -sized paper requires less sensitizer--I don’t know. E.J. Wall recommends sensitizing by immersion in a 3% potassium dichromate solution for 3 minutes.
I have had good success coating fixed out photo paper with a rod, usually adding 1 drop of 5% Tween-20 to 10 ml. of coating solution. The Tween-20 makes coating smooth papers much easier. I use 2 ml. of solution for an 8x10 piece of paper. I’ve also coated with a brush for larger pieces of paper. I dip the brush in some distilled water and shake it out, then pour the solution on the paper and quickly brush it all over, trying to get it as even as possible. I have found that Tween-20 helps when brush coating as well, and that minor inconsistencies in coating don’t seem to make much difference with this process.
After sensitizing, the paper should be dried thoroughly in the dark. I find that I can put it in my drying cabinet and turn on the fan, give it occasional 3 minutes bursts of heat from a ceramic heater, and it will be completely dry in about an hour. E.J. Wall states that the paper only becomes sensitive to light when dry, so damp paper will not make a good print. He also states that paper will never dry properly in a damp environment. He recommends sensitizing with one part 6% ammonium bichromate solution and two parts alcohol in damp weather, and for this sensitizer he recommends coating with a brush. This is called a spirit sensitizer.
Bertram Cox recommends a 5% solution of potassium dichromate, which may be used at full or half strength. He states: “The full strength is better for strong negatives, while the half strength is more suitable for thinner negatives or for negatives which would otherwise give flat results.” He recommends sensitizing by immersion for 3 minutes at 60° F.
Chris Symes describes both the immersion method and the brush coating method. For immersion he suggests a 2.5% solution of potassium bichromate for 3 minutes. For brush coating he recommends a 10% solution of ammonium bichromate mixed with an equal quantity of pure alcohol. He states that paper coated by immersion is more suited to the printing of soft negatives, whereas papers coated by brush are more suited to negatives with greater contrast.
According to William Crawford, increasing the concentration of dichromate increases the speed of printing but lowers contrast. He states that the standard strength of the sensitizing solution with either form of dichromate is 3%, but that it may be used in a range from 1% to 6%, depending upon the contrast of the negative to be printed. Spirit sensitizer may be made by mixing equal proportions of 6 % dichromate with isopropyl alcohol or acetone. Potassium bichromate can only be used with acetone, as it precipitates in alcohol. Spirit solutions do not keep, so mix only enough for immediate use.
Once again I followed Ernie Theisen’s recommendation on exposure time and it proved to be quite accurate. He suggests 7 to 12 minutes. I assumed 7 minutes would be about right for a thin negative, and it was. Most of my dense negatives worked well at 10 to 12 minutes, though one required 15. I’m exposing under a bank of 12 standard UV tubes. The image is clearly visible on the paper, so judging the correct exposure time isn’t too difficult, once you have a little experience. Bertram Cox says: “The image will be of a faint brown colour, and the depth of printing is about correct when details can just be seen in the highest lights.” In my experience, it is better to overexpose slightly than to underexpose.
After a number of failures with very dense negatives, I have realized that negatives with densities above 2.0 are not suitable for the process. My best results have been with negatives with a maximum density around 1.65, using an exposure time of 12 minutes. For pyro negatives I measure the density using the blue channel, and 1.65 prints beautifully. William Crawford states that negatives with a density range of 1.30 are most suitable for oil printing.
The only processing necessary is to wash out the unexposed bichromate solution. Ernie Theisen recommends soaking the print face down in a tray of cold water for 20 minutes before washing. I’m not sure what this does, but it has worked for me. E.J. Wall simply says to wash the matrix in several changes of water until all the bichromate stain disappears. He states that it may be necessary to warm the water in order to completely clear the stain, but warns that the temperature should be raised slowly and should not exceed 90° F. Most contemporary workers recommend that the matrix be dried thoroughly before inking.
Soaking the Matrix
Prior to inking, the matrix must be soaked in water. Ernie recommends soaking for 20 minutes in water at 110° F (43° C). This has worked well for me. I suspect the high temperature is necessary because most of today’s photographic papers have hardened gelatine layers. Be sure to raise the temperature of the paper slowly. Start with water at 80° F. E.J. Wall recommends soaking the matrix for an hour at 70° F (21° C). Chris Symes states that times vary according to the nature of the paper--unhardened papers are generally soaked at 65° F for about 30 minutes, whereas hardened papers may require 85° F.
Inking the Print
The process for inking is the same as for Bromoil, and since I am still a novice I recommend you read a good book on Bromoil printing. Richard Farber’s book Historic Photographic Processes is excellent, as is Gene Laughter’s Bromoil 101, and David Lewis’ The Art of Bromoil and Transfer. Many older books are available online in the Bromoil Reading Room.
Equipment & Supplies
I suggest you read everything you can find on bromoil and the tools necessary for that process, since they are the same for oil pigment printing. Bostick & Sullivan and David Lewis both carry everything you need. Many items can be purchased from art supply and hardware stores.
Brushes. You need lots of round brushes in different sizes. The brush for initial inking should be about 1 inch in diameter and have stiff bristles. Various pastry brushes with hog hair bristles work well, including those from Williams-Sonoma and Carlisle. Home Depot sells a Ralph Lauren “fitch edge brush” which isn’t really fitch (it appears to be hog hair) that is perfect and comes already trimmed at a nice angle. The early bromoil brushes were modified round stencil brushes. Full line paint stores used to carry stencil brushes, but I haven’t been able to find any locally. I found lots of cheap ones at art supply stores, but they all shed hairs prodigiously and so are unsuitable. Brushes for fine detail should have fine hair, such as bear, or fitch (skunk). Badger-hair shaving brushes are said to be good. My experience with one hasn’t been outstanding, but many bromoilists in Britain use them. Brushes can be trimmed to the traditional stag foot shape, which isn’t absolutely necessary, but I find it helps. I went to a local art supply store and bought a Master’s Touch 430 Round Mop, made in Sri Lanka, that has very fine hairs. I trimmed it to the stag foot shape and it works quite well. I now have three of them in different sizes. Gene Laughter claims you can ink with almost any brush and encourages people to collect all kinds and give them a try. All brushes shed to some extent, but the problem with many is that they shed a lot, so you have to be constantly removing little pieces of hair from your print. I should note that the one expensive bromoil brush I bought sheds so badly I have stopped using it.
Brayers. These are rollers with handles. They can be bought at any art supply store. Get several 4 inch brayers with soft rubber rollers, and at least one 1 inch brayer with a soft roller. Foam rollers can also be useful, particularly the white ones from Lowe’s. I find that many matrices ink best initially with a roller--then I can take a brush to them for local manipulation.
Tiles. Six to twelve inch ceramic tiles are usually used for preparation of the ink. You should have at least three of them. Alternatively, you can use a sheet of glass.
Ink. The Graphic Chemical and Ink Company makes very good ink for oil and bromoil--Bostick & Sullivan sell it in smaller tins. Gene Laughter recommends Graphic black litho ink #1803 and #1903 brown. David Lewis has his own brand of special bromoil inks which are very good. I also like the rubber-based VanSon Ink from Holland, which is available from almost any lithographic supply.. You can also use thickened linseed oil with lamp black, burnt sienna, or other pigments added. Ink can be stiffened with ground artist’s soft pastel sticks or magnesium carbonate, and can be softened with linseed oil, plate oil, or (preferably) a softer ink.
Ink knife. An artist’s palette knife with a round end or a kitchen knife will do.
Miscellaneous items. Other items you will need include a roll of Saran Wrap, a kneadable eraser, soft paper towels, a chamois, brush cleaner (naphtha or lighter fluid), masking tape, and dark and light linseed oil.