C.S. POGUE

This high-definition positive-working photo coating is designed for hand brushing onto various surfaces for fine art printmaking, jewelry and fine knife marking, metal decorating, DIY printed circuit board manufacturing and many other exposure-based patterning applications. Spin coating is also possible, however it is wasteful for small runs and is recommended to be used only by professionals. This coating is formulated to flow evenly and self-levels after brushing, resulting in a uniform, streak-free photosensitive layer. It is based on US grown vegetable-based, petroleum-free and bio-degradable solvents, and it is processed using mild aqueous-based developer. It exposes to a broad range of ultra-violet (UV) light sources such as sunlight, black light fluorescent tubes, photo exposure, metal halide, pulsed xenon, and mercury vapor lamps.

D & S Posi-Coat is capable of rendering very high resolution images on lithography stones, ball-grained litho plates, copper, zinc, aluminum, and steel etching plates, and many other metallic and non-metallic surfaces. Features as fine as 5 microns (approximately ¼ the diameter of photo-quality ink jet spots) can be reliably captured when proper coating, exposure, and development procedures and techniques are followed. After exposure and development, the coating is durable, oleophilic (ink-loving), and is an excellent acid etch resist. Baking or heating on a hot plate at 190 degrees F for 10-15 minutes will further improve image integrity and durability for larger editions and prolonged etching times. Some artists may prefer to combine digital or photo-derived images with hand drawings executed on clear film or frosted mylar on the same stone or plate. Multiple images can be exposed to the coating prior to development. Hand drawing can also be added directly to the plate or stone after the photo or digital image has been exposed and developed. ‘Reduction printmaking’ can be accomplished by removing ink from the plate or stone using vegetable oil after one color is printed, re-exposing the coating in areas where the image is to be deleted, re-developing the stone or plate, then re-inking printing all or part of the edition with another color.

Store in a dark, cool environment. Shelf life with refrigeration (45 degrees F / 7 degrees C) is approximately one year. Shelf life at room temperature (72 degrees F / 22 degrees C) is approximately six months. Avoid high temperatures which degrade the photo-sensitive components of the coating.

Grain and level the stone carefully to avoid scratches and uneven surface. Thoroughly wash stone and levigator between carborundum grades to avoid scratches. Periodically check stone for evenness (planarity) during the graining process. The finer the grain, the finer the features that can be printed. For finest detail, 320-grit is recommended. After graining is completed, rinse the stone thoroughly with water under pressure to remove all particles. Dry the stone thoroughly with a hot air stream, such as a hair dryer. It is recommended to allow the stone to continue to dry for at least 12 hours in a dust-free area to insure that all of the moisture is evaporated from the porous limestone.

Counter-etch the plate to remove possible surface contamination. Rinse thoroughly under running water. Dry completely using hot air stream such as a hair dryer.

Remove surface oxidation and other contaminants using an abrasive sponge, such as Norton or 3M 320-grit sanding sponges. Rinse thoroughly by pouring very hot water (190 degrees F / 90 degrees C) slowly over the surface. For optimal results use distilled water. Water should sheet evenly on the plate surface without any signs of beading. Dry the plate thoroughly using a hot air stream such as a hair dryer or a hot plate. (Note: Other cleaning and degreasing techniques can be utilized provided they result in a chemically clean and grease-free surface).

Coating should be applied in a well-ventilated area. Eye protection and gloves should be worn. See Material Safety Data Sheet (MSDS) for further information.

To achieve optimum results it is important that the coating thickness be uniform at all points on a given surface. The stone or plate should be coated in a dust free, room lit with yellow fluorescent tubes or yellow ‘bug’ lights. Darkroom safelights are also acceptable. The stone or plate should be resting on a level surface on blocks above the counter surface. Because the coating dries relatively slowly as it self-levels, it is advisable to cover the stone or plate with a dust shield while it dries. The dust cover should prevent dust particles from reaching the surface but must allow free evaporation of the solvents. A fine silk screen or wooden frame over which is stretched a sheet of lint-free cloth will suffice.

The following practices will result in consistent ‘standard’ coating thickness so that exposure requirements will remain consistent from exposure to exposure.

Immediately before coating gently wipe the surface with a lint-free cloth to displace any dust particles. Excellent results can be obtained by rolling the surface with several passes of a peel-off lint removal roller readily available at hardware stores and supermarkets.

If only a portion of the surface is to be coated, mark the image area(s) on the stone or plate using a red conte crayon.

Determine the total image area in square inches by multiplying the length by the width. (If measuring in centimeters, divide the result in square centimeters by 6.5 to obtain the area in square inches). Round up or down to the nearest 25 square inches.

Divide the image area in square inches by 25 to determine the number of eyedroppers of coating required for ‘standard’ coating thickness. Use one eyedropper full (approximately 1 ml) of coating per 25 square inches of image area to be coated.

Squeeze the rubber bulb on the eyedropper completely when drawing coating into the glass eyedropper; do the same when dispensing the coating onto the image area surface.

For large image areas, measure the appropriate volume of coating into a glass graduated cylinder, using 1 ml of coating per 25 square inches of image area.

Dispense the appropriate volume of coating onto the image area surface using roughly evenly-spaced lines.

Use a clean natural or synthetic bristle brush sized appropriately to cover the entire image area within about 10-15 seconds. ‘Load’ the tips of the brush bristles with additional coating from the eyedropper before spreading the measured amount. Using light brush pressure with the tips of the bristles only, spread the measured coating evenly over the image area in a crosshatch pattern, first going in one direction over the entire image and then at right angles to the first brushing. Repeat along both diagonals. Do not over work the coating as excessive brushing time may allow the coating to begin drying and create streaks. Some light streaking may be visible after four passes, but this will even out as the coating self-levels.

Place the dust shield over the stone or plate and allow it to dry for 12 hours or longer in darkness to insure that the solvent is evaporated from the coating.

The sensitized stone or plate is now ready to be exposed; alternatively it can be stored up to several months in a cool, light-tight environment.

In order to successfully transfer the finest features and sharpest edges of the image from the film positive to the stone or plate it is necessary to maintain intimate contact between the light-blocking materials and the coated surface. The ‘emulsion side’ of the film positive or the ‘ink’ side of the clear film must therefore be placed against the coating. In the case of graphite drawings on frosted mylar, the graphite side of the mylar should contact the coating. If the light-blocking material of the film positive is not pressed tightly against the coating, exposure light may ‘leak’ or refract around the image edges, creating ‘flare’ and loss of fine details and sharp edges.

A vacuum exposure system is ideal for this purpose and can be simply and inexpensively improvised by use of a Space Bag (costing around $10), a piece of nylon screening, and a vacuum cleaner. (See diagrams and photos on D & S Graphics web site).

A suitable alternative for truly flat surfaces such as intaglio plates is to place a sheet of glass over the coated surface with the film positive sandwiched between the coating and the glass. Thicker (1/4”) plate glass is preferred to window glass because it is not as easily broken and the extra thickness increases pressure on the film/emulsion boundary. It is also possible to place small weights on the glass outside the image area to improve contact.

For best results it is STRONGLY RECOMMENDED to conduct test exposures to determine the appropriate exposure time for your particular light source, distance from light source to stone or plate, etc.

If using lithography stones, grain several small test stones (broken stones 3 by 8 inches will suffice) using the same grit number of carborundum used on the larger edition stone. Coat the test stones at the same time as the printing stones and allow them to dry as above. If using ball-grained plates or intaglio plates, coat small test samples and dry as above.

It is STRONGLY RECOMMENDED to use a 21-step Stouffer Scale ($7 to $10 on line) for calibrating your standard exposure time, at least for the first test. You will also need some small pieces of UV-opaque masking paper for the tests, such as Goldenrod paper, Rubylith film, black matte board, heavyweight aluminum foil, etc. for blocking the exposure UV light. Place the Stouffer Scale with the emulsion or film side against the coating on the stone. Cover the rest of the stone or plate with the masking material and press glass or vacuum and expose. Start by making three test exposures: 1). half of your estimated exposure time; 2). your estimated exposure time; 3). double your estimated time. After development of the test exposures, use the Stouffer Scale directions’ correction factors to obtain the correct exposure time for your set-up.

Always wear eye protection and waterproof gloves when handling alkaline developer. See Material Safety Data Sheet (MSDS) for further information.

This coating develops best by immersion and slow agitation, rather than by scrubbing or vigorous agitation.

When developing a lithography stone, place the stone image-side down in a developing tray. Place four Q-tips between the stone surface and the tray at the corners to slightly separate the stone from the bottom of the tray.

Pour a sufficient amount of developer into the tray so that the coated surface of the stone is submerged by at least 1/8.”

If using plates, simply place in a developing tray and pour sufficient developer to submerge the plate by at least 1/8.”

Gently rock the tray back and forth in the sink for about 60 seconds. Remove the stone or plate and set it image-side up in your sink or in a clean tray. Pour some fresh developer over the coated surface and gently rub the surface with a cotton pad or soft cloth to insure complete development.

When the image is fully developed, rinse everything with plenty of water including the stone or plate, tray and sink.

Gently blot or squeegee the stone or plate and dry with a hot air stream, as from a hair dryer.

If using lithography stones, mix up a mild gum etch (4 drops nitric acid to one ounce of gum), apply it to the developed stone and buff it tight with cheesecloth.

If using ball-grained or intaglio plates, gum etch is not necessary.

Allow to dry for at least five minutes; then take the stone or plate to an inking station. Dampen the stone or plate with water and roll it up using a tacky ink.

Examine the results of the inked Stouffer Scale image for the highest clean step. Optimum exposure of this coating will result in a clean Step 3 after inking. Refer to the Stouffer Scale instructions for a simple correction calculation to your test exposure before exposing your actual printing stone or plate.

Insufficient UV exposure will result in background toning on the lithographic press and/or uneven etching in acid resist applications. Excessive UV exposure will result in a loss of fine features.

The exposure latitude of this coating is considerable, and it is preferable to be slightly over-exposed rather than under-exposed for best printing and etching results.

For reference, proper exposure of plates with our recommended ‘standard’ coating thickness using sunlight through plate glass and ink jet film positive in the northeastern US has been in the range of 10-15 minutes.