Making One's Own Waterless Positive Plates
Positive litho plates are becoming more and more common amongst fine art printmakers because of the ease of doing editions and the assurance that an edition can still be completed if a plate is lost for some reason. Registration of Mylars with the use of a pin registration system will produce prints of better quality with much less trouble. I have used three brands of commercial positive plates and have found all of them to be of high quality, though there were slight differences in their characteristics. It is very easy to use these commercial plates with my waterless process and only the developer need to be purchased when placing your order. After exposure and development, a coat of silicone is applied to the plate and later the image is washed out with the acetone/diacetone alcohol solution, or some cases alcohol.
Since my present series of lithographs have required a large number of plates because of the many colors I use in the edition, the cost of plates started to put a restriction on the number of editions I printed. I do not use positive plates for all the colors I need, but I do use this more expensive component as required. I had found a way to use the back of the common ball grained plates (see paper of reusing plates), which I used for toner washes and flats drawn with Sumi ink. I also use many of the cheaper smooth commercial offset plates for direct imaging, but there were many images that could have used Mylar positives. With the knowledge of reusing plates, I decided to find a way of making my own photo emulsion coating for the plates on hand. My first experiments were directed to making a plate that could be used similarly to the commercial Toray plates, that some printmaker use. This required that the ink rejection silicone layer be place over an emulsion before the exposure of the plate.
Theory behind my early research
If a negative working plate is coated with silicone before exposure to a positive Mylar image, then the clear area would be hardened and not be removed by the development of the image ---- the silicone would be still on the plate to reject ink. Only the unexposed areas protected by the opaque image would be removed, producing a printed mark. This was probably the approach taken by 3M and later by Toray in researching their products. With this in mind, I tried diazo negative coating and other traditional negative emulsions. While the diazo wipe-on method produced the worst plates, others materials produced good enough results to encourage to me continue with the research.
While taking my apprenticeship as a graphic artist in a printing plant in the 50's, I learned many aspect of lithography as part of my training. We made two types of litho plates, depending on the quality of printing job on hand. The fastest and cheapest were the plates that used ammonium dichromate as the photo sensitizer for egg albumin. The other type was a deep etch plate that used gum Arabic for its colloidal protein content. This type of plate was more expensive to make, but produced superior results. Amongst the many protein containing materials that I tried for my positive plates were egg albumin, fish glue, casein, polyvinyl alcohol and gelatin. While I had used egg albumin many years before in doing printmaking at my home studio, I had used a whirler system to apply an even coat to the much smaller plates I was using at the time. I intended to find a coating system that was simpler, yet effective enough to be used at schools and small print shops. I tried foam sponges and a pad of velvet cloth to spread an even coat over the larger plates I now use - unfortunately, egg albumin has a tendency to froth, leaving me with bubbles and pinholes, and an imperfect plate surface. In time I perfected a spreader system that worked effectively.
The use of casein was common to printing plants before the introduction of diazo powders and presensitized plates. Casein is a product of skim milk and was at onetime a popular wood working glue that could produce waterproof joints. The advantage of casein is that it takes a lot less exposure to harden the emulsion than those made with other proteins. Today, casein is no longer available in hardware stores or other suppliers. Because of the small 110-volt arc light source I use, I wanted the shorter exposures that casein provided. I remembered reading of a method used to make casein from milk curd and different alkaline compounds. After looking through my reference material, I decided to produce a crude casein from dry curd cottage cheese, which contains the least amount of milk fat. At the grocery store, I also bought a bottle of ammonia water and one of Mrs. Stewarts Liquid Bluing. By mixing the ammonia with the curd, it made a very effective liquid casein that could be diluted and sensitized with ammonium dichromate. While I would have preferred to use the less toxic diazo powder, it was not available to me as a separate compound, while I did have a good supply of the more active ammonium dichromate.
In my research, I have found that fish glue works well in my formulation, but the longer exposure time made it less desirable for my studio. If you have access to a powerful exposure unit, then other colloidal proteins can be used. Fish glue may be as hard to obtain these days as is commercial casein.
Making Crude Casein
Secure dry curd cottage cheese from your local grocery store, trying to find one that contains the least amount of milk fat. Household ammonia is the alkali that is best suited for this purpose, as an excess of ammonia is required when using ammonium dichromate emulsions. This keeps the casein emulsion useful for a longer time, as long as ammonia is present in solution. I would suggest you break up the curd into smaller particles so that the reaction will be faster and produce a smoother product, which requires less stirring. Pour the ammonia over the dry curd and mix with a non-metal implement. In a couple of hours, the change will have taken place and you should have a honey colored colloid that may be rather viscous, depending on the amount of liquid added. To dilute it, you could use water, but I suggest some of the Mrs. Stewarts Liquid Bluing for a start. Since blue dyes allow the ultra-violet rays to pass, you will have a good indicator for the application of your emulsion, without have it increase exposure time. To prevent the putrefaction of the emulsion, add some disinfectant to the solution. I prefer Dowicide A, but Lysol or Carbolic acid should work as well. The viscosity of the emulsion is important, but can be a matter of adjustment for your method of working. After the ammonium dichromate solution was added, I have found that a specific gravity of about 1.035 gave good results for my procedure.
While this simple emulsion worked well for exposure and development with water, I found that the silicone tended not to bond to it as well as I wanted. I did finally make use of the emulsion by adding it to the colloid in screen emulsions. It still becomes an important part of the coating process.
Sensitizing the emulsion
While diazo should be the sensitizer of choice because it is less toxic, it may be hard to acquire as a separate compound. Since it is less effective in converting protein to a hardened state, I preferred to use ammonium dichromate, which is the fastest of all the dichromate salts once used in emulsions. To have some quality control of the emulsion, it is a good idea to use a measured quantity of sensitizer. You could use either a saturated solution, or the more popular 20% solution used in printing plants. I chose to use a 25% solution that is made by dissolving 25 grams of ammonium dichromate in 100 cc. of water. This is added to the casein to make up about 12.5 % (1/8th) of the total volume, which in the end should have a specific gravity of 1.035. The ratio of dichromate to protein solids has an effect of the sensitivity of the emulsion, so the percentage I used is a starting figure, but at the upper limits. Since there should be plenty of liquid ammonia still within the casein, addition of this stabilizing chemical is not necessary. Water or a strong blue dye is added to bring the viscosity to a specific gravity of around 1.035.
Modification to the emulsion
Because the silicone was not bonding to the slick surface provided by the hardened casein, I started to look for other practical emulsions. Screen emulsions come prepared and only need the mixing in of diazo as a sensitizer. By diluting an emulsion with an equal amount of water, I found it could be spread quite evenly and produced a good image on exposure and development with water. It turned out to be extremely quick and easy to develop when compared to the casein exposed emulsion. The fillers used in the commercial screen emulsions provided a tooth for the silicone, and there was also a slight tendency for the silicone to penetrate into the surface. This provided a good bond, but all was not well. When using VanSon rubberbased ink as I recommended for siliconed plates, there are times when the ink color has to be adjusted and the plate cleaned for the new ink. Since acetone is the only solvent that will effectively remove the ink and not damage the silicone, the plastic component within the screen emulsion would not hold up to this solvent, and I would lose the silicone. While it is possible to remove most of the ink with numerous printings on newsprint, I chose to find a better method. From the numerous attempts I made, I realized that a modified screen emulsion might work better if the casein's characteristics were added. I also saw that the application of silicone over the emulsion may not be the best approach.
A modified deep etch plate
Because of my apprenticeship experience in helping the plate department make offset printing plates, I understood that the use of positives were needed for that process. I decided to adapt the procedure, but replace the materials. The deep etch process uses any number of different sensitized colloids exposed to a positive. This hardens the background areas and allow the image alone to be removed with appropriate developers. After the image was released, the plate was then washed with anhydrous alcohol to make sure no water damaged the stencil. Deep V lacquer was rubbed into the image and reinforced with developing ink and rosin/talc mixture. Next, the plate was placed in water and soaked until the hardened emulsion came off. The plate was then gum etched and sent to the pressroom.
Using this concept, I included this extra step to produce a better plate. After exposing and developing my plate with water, I applied deep etch vinyl lacquer to the image areas. I didn't reinforce the lacquer with developing ink, but removed the hardened screen emulsion with sodium metaperiodate, the standard screen emulsion remover. Because of the nature of screen emulsion, the lacquer would combine with the plastics and make it very hard to remove the background stencil. This is where I decided to mix the casein and screen emulsions to produce a surface that was better than either alone. While diazo might be preferable, the dichromated casein proved more than adequate. I understood that the diazo screen emulsions are slightly acidic, while my casein emulsion was definitely alkaline. On doing some research into diazo, I found that ammonia seemed compatible with the material and it was acidified only for storage reasons until mixed with a colloid. In practice, my mixture worked very well, after I allowed it to sit for enough time to eliminate the slight foam on the surface. I would reinforce the ammonia sometimes.
Fine tuning the process
The coating of plates
Because of the nature of the modified emulsion, I found I had to improve the coating system to give me as smooth a surface as possible. The carrying capacity of the commercial paint spreader pads I bought was not sufficient for even mid sized plates, so I designed my own system. Build with a piece of 1 X 4 X 6 inch mahogany, it was smoothly beveled on the two longer sides. One side was given a greater upsweep to allow better manipulation of the plate surface. A piece of the double-sided fuzzy blanket material was tightly stapled to the pad. This fabric (Velux) is commonly used for blankets in hotels and sold in fabric stores as remnants. Another and maybe even better material is Arctic Fleece or Polar Fleece (basically the same material), an insulation fabric used in winter garments; it is also available as remnants. A short handle made of one-inch dowel, screwed on at 45 degrees, finishes the applicator
The emulsion is poured into a small photo tray, and the pad dipped in to just wet the bottom. The excess is scraped off the fabric, as well as off the edges along the ends. The plate is covered from end to end, with the passes slightly overlapping. Under a yellow bug light that is placed low enough to allow you to see the reflections on the surface, the surface is carefully covered until no heavy deposit lines are visible. The flat surface of the spreader paddle is used to initially cover the entire plate, then the upswept edge is used to even out the surface. As you go over the plate with the curved edge, you have better control over pressure. The entire plate does not have to be covered, only the image area. Make sure there are no fine lines with the emulsion missing - this is easily seen from the reflection of the shiny metal surface. The addition of the blue dye allows you to see any imperfections in the thickness of deposit. With care and practice, this method will produce good enough coatings to use with this modified deep etch technique. Allow the plate to dry, with enough time for all the ammonia to escape from the emulsion. Use yellow bug lights in the work area.
The emulsion mix
I have tried four different screen emulsions and all worked well as far as I was concerned. They required slight adjustment as to viscosity, but that could be due to their age and storage. The one formulation I have settled on is the following. I first dilute the sensitized screen emulsion in an equal volume of water. To this I add one part of my sensitized casein emulsion, to four parts of the screen mixture. Having added blue dye before, this should make it dark enough for observation under the yellow bug light. The finished mixture should have a specific gravity of about 1.035, but you may find thicker or lighter solutions work better for you. I allow the mixture to stand until the foam is no longer being produced because of the acid/alkaline reaction. If you can get diazo powder, I would suggest you try it as it is considered to be a better material. I found that the screen emulsion was too rough and not perfect to use alone; the plastic component in it also reacted to the solvents in the vinyl lacquer. The glue casein also helped produce a smoother surface for applying the lacquer. While other water soluble glues could work as well, I have decided to stick with my crude casein with its shorter exposure time.
Exposure of the plate
I would have liked these plates to be able to retain the extremely fine detail of toner washes, but, while the emulsion can produce the textures, the vinyl lacquer does not stand up to processing as I have devise the procedure at this time. I plan to work on this deficiency. Flats and many textures can be easily reproduced, making these plates an inexpensive way to apply colors to your editions. Since my plates contain dichromate sensitizer, I have to consider dark hardening, something that diazo has eliminated. I use the sensitized plates on the same day I coated them because of dark hardening.
Use any effective UV point source with a vacuum frame, like for commercial plates. Try and keep some sort of record of your formulation and exposure times for use in future editions. A light integrator is a helpful tool in controlling precisely the exposure of your plates, especially where delicate tints are concerned.
Development of the emulsion
Under yellow lights or subdued incandescent bulbs, flow water over the surface for a few seconds. You will immediately notice the image area taking on a lighter frosty look. Use a very soft plush fabric to gently go over the image, until the metal is clear of any material. Do not rub hard, but make sure all the loose emulsion is off the plate surface, as it can cause tinting later. Tilt off the excess water and gently pass a squeegee to remove the rest. Blotting dry with newsprint is another option. A properly exposed plate will take quite a bit of rubbing with a gentle fabric, but can be damaged with a heavy hand. Let the plate dry to allow the emulsion to become firm. A pad made with scraps of fake fur from a fabric store, works fine for gently developing the exposed plate. I use a rubber band to hold the fabric on a small piece of 2 x 4 lumber.
Masking areas that have no emulsion
Before the lacquer is applied, it is possible to mask areas with a simple water soluble glue solution to prevent the lacquer bonding to the metal surface. This procedure may be necessary if you missed some areas in you emulsion application, or dust and other blemishes become visible. Use a reflected light to notice the spots to cover. If you use color separation positives produced from your computer, you will probably use some form of registration marks to assemble the Mylar overlays. These will show up after the development of the plate, but can be eliminated from the print by covering them with Sumi ink and some water soluble glue mixture.
The vinyl lacquer
I found that the normal viscosity of Handschy lacquer was too thick for the best application over the hardened emulsion. I diluted the lacquer with about 25% of butyl carbitol, which also acted as a good drying retarder. The diluted coat of lacquer was now even harder to see, when the hardened emulsion was removed. To improve image visibility, I added more red dye in the form of Eosin stain. Other dye materials might be better than this water/alcohol stain I already had on hand. The dye was dissolved is a small amount of alcohol and added to the diluted lacquer. I read that boracic acid added to plastics in solution will make them tougher to abrasion. I have no way to test this, but I have added about .5 % as recommended, with no ill effect. The vinyl is spread over the developed plate and gently buffed to as even a film as possible. This becomes important when it comes to removing the hardened emulsion. I have found it best to keep the edge of the lacquer a good distance away from the image, as this may turn out to be slightly heavier in application right at the edge. It will be more difficult for the emulsion stripper to get under the thicker lacquer layer and may require harder rubbing. If too close to the image, you might harm the lacquer within the image.
Apply in the lacquer
Using facial tissue or a soft cloth, apply the modified vinyl lacquer much like you would with traditional lithography. Spread the lacquer to an even layer, but a lot thicker than you had used for a traditional application. Leave some room between the image and the edge of the lacquer, as this will likely be a heavier coating at the boundary. I prefer to use my paint stripping heat gun to quickly dry the lacquer, as the butyl carbitol takes a long time to evaporate. You will see the change in the lacquer as it dries.
Removing the hardened emulsion
Use sodium metaperiodate, the generic stripper for most screen emulsions. I use a urethane foam sponge and cover the entire surface where there is emulsion. The lacquer will protect the emulsion for a while, but let it sit for a few minutes to react, then gently rub those areas. If your modified emulsion is of the right formulation, the lacquer will start to come off in just a few minutes. It will take more rubbing where the lacquer is thicker along the edge of your application. The pink of the image will show against the metal and allow you to see how you are progressing. I flush off the stripper with water and use a squeegee to get rid of it. One can see if all the areas are clear of emulsion as these will show as a darker stain; reapply stripper to those regions. I have found that a much less concentrated solution of the expensive metaperiodate powder is needed than for screen printing. Start with about one teaspoon of powder to a quart of water.
It is important that you apply a very diluted wash of sodium silicate over the bare metal, to allow the caulking silicone to better bond to the surface. If too strong of an alkaline is used on the surface, it can damage the lacquer and destroy your image. My solution is about 9 pH or less, but it could be made weaker I think. Flush off the silicate after just a few seconds and dry the surface. It is now ready for coating with silicone.
Checking the vinyl image
All should be well, but it might be a good idea to carefully examine the image. You should be able to see the slightly pink coloring on the reflective metal surface, and notice if the lacquer is missing for some reason. Use the same Sumi ink and glue mixture I recommended for covering emulsion blemishes, or use a solution of shellac in alcohol.
I dilute my silicone much more for this process than what I recommend for drawing on grained plates. Since the smoother surface has very shallow depressions when compared to ball grained plates, less silicone would cover the surface well enough. Buff the silicone to a smooth layer and allow to air dry, since it will take very little time for curing in such a thin layer. A second coat can be applied, but be careful and not rub too hard in spreading the new silicone and allow sufficient time for the first layer to cure a bit. I use a folded piece of facial tissue to apply silicone to the positive plates as I have found it superior to the foam rubber, which as a tendency to act like an eraser. Let the plate cure as well as possible before attempting to develop (wash out) the lacquer in the image.
Development of the image
Use your acetone/diacetone alcohol solution for taking out the lacquer and revealing bare metal. If your lacquer was not as thick as it should have been, there may be areas that will not take water as well when you wash the plate. Go over these areas again with acetone, taking care not to harm the silicone edge. Some strong industrial cleansers may also help to retrieve these areas, but remember the silicone is still not well cured and easily damaged. When the entire image takes water, which you can see as a reflection, the plate is dried and ready for printing.
The plates are just as robust as my other waterless plates and print large editions. If you encounter areas that want to take ink, these can be blinded with a very diluted solution of caulking silicone in white gas. This allows the solvent to quickly evaporate, leaving a very thin silicone coating. Apply with a facial tissue and let stand for a couple of minutes, then buff with a dry section of the tissue. Heat can be applied if the area is away from the image.
If you are not careful in preparing and handling the metal surface, surprises can appear as tints, smears or lines, just like in ordinary lithography. Keep the area you work in as clean as possible to prevent contamination of any kind. I have found that it takes very little of a water-soluble material to become an image or blemish on your plate, if you are careless in handling the plates.
Reclaiming the plate for reuse
This is the nice part of this technique, the continued reuse of the plate. Because the silicone layer is very thin, the silicone stripper can be very diluted as well. First remove any ink with acetone or lacquer thinner, making sure the surface is free of oil. I use a mixture of hydrochloric and phosphoric acid, with a touch of ammonium bifluoride. The bifluoride helps in breaking down the silicone layer quickly and not allow the image to be etched into the metal. To about a gallon of water, I add two ounces each of the acids, then include a tablespoon of ammonium bifluoride. This gives me a solution of about 1.5 pH. I apply this with a pad made from carpeting glued to a piece of wood. Make sure you wear some sort of hand protection from the bifluoride in solution. I sometimes sprinkle aluminium oxide grit to give the plate some grain, if I feel the surface it too smooth. I chose aluminium oxide rather than using silicon carbide, as the latter will be attacked by the fluoride solution. It should be very easy to reclaim the plate as long as the silicone was not applied too thickly or ink has been allowed to remain on the image. Apply sodium silicate solution if you want to use the plate next for direct imaging. Flush the surface with water and dry. The plate is ready for reuse for direct drawing or as a positive plate.
Using this process for making plates from negatives
I have had mixed results using this emulsion for negatives instead of diazo wipe-on emulsion. The same positive emulsion mixture was applied on plates and allowed to dry. The exposure was made through a good negative and developed in plain water. This left the hardened emulsion in the image area. Silicone was applied over the entire plate and buffed down as for a normal plate. After the silicone cured, the plate was developed with the sodium metaperiodate solution used for making positive plates. I have experimented in trying this process on the back of used plates, in the hope of saving money and getting rid of the diazo developer. It would be important that the plate be subcoated with diluted silicate solution before coating with silicone, to better hold the rejection layer. I must admit that the commercial diazo material produces and holds superb fine detail.
By using this method, one would eliminate the toxic solvents in the diazo developer supplied with the commercial process. Plain water is used to develop the plate and metaperiodate to release the image from the cured silicone. Neither is dangerous in comparison to any other commercial material used for negative systems. Once the silicone is bonded to the metal surface, the plate is a robust as any waterless plate.
Because of the uncertainty of success with this technique, I continue to use the supply of diazo material I have on hand. As time permits, I will do more research by trying different emulsion formulations and try other methods. My aim is to eliminate the toxic developer now used with commercial diazo.
While some may consider making ones own plates taking things too far, in view of the many excellent commercial plates on the market. These commercial plates are intended to be used only once and can become a major expense, if a large number are needed in an edition. Today, the packaged product is considered the ultimate choice because of high standards of production, but this entails a price many may not want to pay.
Positive plates and use of images on Mylar is now an accepted part of printmaking. Most of the successful printer/publishers are using them for a good reason. I have found printmaking faster, easier and cheaper, using these 'home-made' plates, and will continue to utilize them whenever I can. While I still think commercial plates produce the best fine detail from toner washes, these plates are perfect for most of the plates I need for an edition. Flats, coarser textures and line images work well with these plates, reducing my plate costs to a fraction of what it was before.
You will have to first perfect the recycling of plates as covered in my other paper, before attempting this process. You can also try thicker commercial aluminium sheets as longer lasting plates. Making one own photo plates was a standard operation when I started my lithographic apprenticeship in the early 50's, and was just another part of the craft that one learned. We are supposed to be masters of this "diabolical craft", controlling all aspects to get the best image possible. While different, this is no harder than producing editions from grained limestone by traditional lithography.
This information is copyrighted material, but I urge printmakers to copy the paper to hand to others interested in the method. Publication in any commercial or educational journal is prohibited without permission, and the only reason I reserve the copyrights.
Department of Art and Art History
University of Saskatchewan
Saskatoon, SK. S7N 5A4