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Studio Camnitzer

founded in 1971

Ecoresist. Technical information and instructions for use

Studio upstairsAfter an interruption in production, Ecoresist is available again in a better version. The Studio, however, will not distribute it anymore and we refer you to the manufacturer in Italy (address at the end of these instructions). We continue working with it in the Studio, will keep the instruction sheets on the web and will keep updating as needed.

Ecoresist is a negative photo-resist: it uses positive transparencies and the plate is etched in the unexposed areas. The photo-resist itself has a solvent base that has the same toxicity rating of mineral spirits normally used in art tasks. Toxicity is further reduced by the fact that there is no separate dyeing process and that the development of the plate is water-based. The emission of vapors only occurs during the application of the resist onto the plate—during which good ventilation should be available—therefore cutting exposure to vapors in half compared to traditional solvent based processes. If handled correctly, there is no need for contact with the resist, making the use of gloves unnecessary while handling the plate. While not yet the absolutely toxic-free product we would like, Ecoresist thus seems, for the moment, to be the best compromise between the toxic high-resolution photo-resists and the relatively non-toxic, but cumbersome water based films. Unlike the latter, the etched image has minimal loss of information and does not need pre-thinning to achieve a good etch. Over the so-called “solar plates,” Ecoresist has the enormous advantage that the plates can be re-exposed and re-etched until perfection. It should be noted, however, that for one-shot and one plate projects, the resolution of solar plates is higher.

Ecoresist can be used on any metal, but the information in the following pages was compiled using brass plates subsequently etched in a ferric chloride solution of 15 degrees. Ferric chloride is usually sold in a 42 Baume solution, and if there is no densitometer available, a solution a little stronger than of 1/3 ferric chloride and 2/3 of water may be used. No matter what, etching times should be tested.

Ingredients and toxicity rating

The principal ingredients in Ecoresist are Propylene Glycol Monomethyl Ether and Xylol. The propylene family is the safest of the cellosolves (as opposed to the ethylene group used in other photo-resists and described by McCann in his hazardous art materials list). The toxicity rating of the Ecoresist chemicals is 4—moderately toxic—the same as mineral spirits, turpentine, hard ground and ferric chloride etch. Permissible exposure limits for this category are 100 to1000 parts per million of air. KPR (Kodak Photo-Resist), nitric acid and Dutch mordant, on the other hand, are rated 5 or highly toxic, with permissible exposure limits of only 10 to 100 per million. A toxicity of 6 (benzene, potassium dichromate) is extremely toxic and should be below 10 parts per million. (See Moses, Purdham, Bowhay and Hosein, Healthy and Safety in Printmaking, Alberta Labor Occupational Health and Safety Division, Edmonton, 1978). Permissible exposure limits refer to amounts judged to be below any threat to human health.

Dilution

Ecoresist is a product designed for industrial use and comes in three different strengths to fit different methods of application: Ecoresist-100, Ecoresist-80 and Ecoresist-60. Ecoresist-60 is the most economical one (simply because it contains more solvent and less photo-resist) and comes the closest in viscosity and flow quality to what we are accustomed to with the traditional resists after their dilution for use. The viscosity is also appropriate for spraying. For further dilution, there is an Ecoresist solvent available from the manufacturer, but it does not seem needed for our purposes. We will therefore only discuss Ecoresist-60 here.

Degreasing

As is the case with all photo-etching procedures, the plate has to be perfectly degreased. A good scrubbing with fine grade pumice powder (available at hardware stores) is usually enough. It is advisable to use salty vinegar (a tablespoon of salt dissolved in a quart or liter of vinegar) to rub the powder in order to remove oxide marks. If pumice powder is not available, any kitchen scouring powder will do but will require extra care in washing to eliminate residues of detergent. The plate is properly degreased if running water over leaves a smooth unbroken film on the surface. If there are oxidation marks on copper or brass plates, a further rubbing with salty vinegar will eliminate the spots. The plate should be rinsed well, dried with a hairdryer and allowed to cool down. Any trace of pumice powder left on the plate will be picked up by the brush and eventually mixed into the Ecoresist. So, make sure the plate is dust-free.

Before re-coating for further exposure and etching, it is advisable to also use the salt-vinegar solution for a final rubbing. Any trace of grease or dirt will interfere with the resist.

Coating

We have found Ecoresist-60 to have the right consistency to be brushed onto the plate. This makes the product extremely economical since, unlike flowing, the waste is practically zero, reduced to what may be left in the brush after the coating is finished. It is enough to coat an area slightly bigger than the image. The rest of the plate (including the back) can be protected with asphalt ground before the etch bath. It will help to leave an edge of about ¾ inch (2 cm) since the border of the plate tends to accumulate more resist and harden less during exposure. This will also leave room for registration marks when working with color separations or multi-plate etchings. Allowing the resist to dry on its own will minimize both this accumulation and the loss of usable surface

The plate should be placed on a jar or cup (or many of them with the same height) so that the edges of the plate go well beyond the support surface. If the support surface is bigger than the plate (as a table might be) some resist will go under the plate and be wasted.

A small amount of the resist should be poured into a glass jar and then, from the jar, brushed onto the plate with a good soft wide brush (1½ inches or 4 centimeters). The brush should be dipped in the jar to hold a generous amount of Ecoresist, held as flat as possible against the plate, and brushed without exerting force (basically laying the resist rather than painting withit). Just the weight of the brush will do. Brushing should be performed gently avoiding bubbles, streaks and dust as much as possible. Bubbles can be broken by gently blowing on them. If needed, while still wet, the plate can be brushed with more resist at a right angle. This step is taken not so much to add resist but to even out the surface. Letting the plate stand to dry alone will improve the evenness of the surface. Some unevenness is to be expected, but there should be no abrupt changes in thickness or uncovered streaks. Once the brushstrokes have fused together, the drying process may be completed with a hairdryer set on hot and with the air stream medium to high. The dryer should not be too close (12 inches/30 centimeters or more according to power), or initially directly aimed at the plate, in order to avoid disturbing the wet surface and the creation of ripples. Normally, the resist should have started its drying process by the time the brush strokes have merged (two to three minutes). The plate loses its shiny wet look once it is dry (one to two minutes later) and acquires a shiny varnish look instead. At this point, the edges may still be wet and should be wiped with paper towel (also under the plate). If after it dried, the plate does not have a satisfactory look, a second coat can be applied over the first one. In this case there will be a difference in the thickness of the photo-resist and exposure will have to be somewhat increased. If after dry there are dull areas, it is advisable to recoat the plate. The dull areas are porous and may allow for under etching.

If the coating process is performed with a minimum of care, there should be no reason for any contact with the skin. Gloves thus are an optional item, not a required one. A good protection is achieved covering the hands with liquid soap and letting it dry. At the time of touching the coated plate, only the edges (above and under the plate) may still be wet. Using a piece of paper towel in each hand to lift the plate will protect hands and serve to wipe the edges dry. It is advisable, the same as with all mineral spirits, to work under good ventilation. The speed of application and of drying of Ecoresist-60 keeps the exposure to fumes to a minimum.

If possible, the coating and drying should be performed under a dim incandescent light (15 watt bulb close or 25 to 40 watt far away). While the plate is wet it remains light tolerant. As the resist dries it becomes more critically sensitive.

The ideal temperature for the process is between 65 and 80 degrees Fahrenheit (19-25 C). The activator in the photo-resist tends to separate below 60 degrees Fahrenheit (15 C) but reconstitutes when warmed up to 80 F (25 C).

After finishing coating with the brush, the brush can be easily cleaned with alcohol. The cleaning should be done thoroughly to extend the life of the brush. If there is photo-resist left from the batch separated for use, it can be returned to the original bottle (as long it was kept in its pure original state and dust free).

Transparencies

Any decent transparency will give satisfactory results. We have increasingly shifted from the darkroom to the computer. Transparencies printed both by laser printers and jet ink printers work without problems, as long the pigment is black. Some older jet ink printers use bluish ink, which is less protective against the ultraviolet light used for exposure. We have used low-end Hewlett Packard laser printers and Epson and Canon jet ink printers with good results. Some jet inks and some transparency material are humidity sensitive. If there is a fine halftone on the transparency, it should be exposed shortly after printed (giving time for the ink to dry) (it is advisable to blow-dry the transparency before making contact with the sensitized plate). Otherwise the dots may become blurry (something that will pose difficulties with any photo-resist). New generations of jet ink transparency stock, like that manufactured by TDK, have a diffusion-prevention coating that provides longer life and blur protection. The ideal transparencies are still those made by a service. The loss of information that homemade transparencies have (ca 10%) can be compensated by printing two copies of the transparency and doubling them up for exposure. It is always useful to have two or more versions of the image; one with attention on the light areas and one on the dark areas, which can be used in separate exposure and etch steps. Loss of information thus can be compensated with selective reexposure from different transparencies. The presence of registration marks will be very helpful for correct alignment. We have found that (among cheaper printers) the constancy of registration marks is more trustworthy on jet printers than on laser printers. Due to the heating of the laser ink, transparencies tend to expand at different rates. Jet printing is a cold process and therefore the transparencies remain exact. The registration marks printed through Photoshop tend to be a little too thin. You may draw your own marks on the master image using Photoshop’s pencil function and using 8 pixels for thickness.

Exposure

Studio upstairsAny actinic light source (that is, high with ultra-violet wave length) will work. The spectral sensitivity of Ecoresist is within a range of 360 to 430nm with a peak at 400nm. If the plate is exposed through a transparency without perfect contact (that is, not using a vacuum table), it is important to use a point light source. “Point light source” refers to bulbs as opposed to fluorescent tubes. A bulb casts sharper shadows, which can bridge gaps between the transparency and the plate. A fluorescent lamp throws scattered light, which will seep into the areas with poor contact. This becomes particularly noticeable with halftones.<./p>

The time of exposure depends on a) the thickness of the application of photo-resist, b) the power of the light source and c) the distance of the source to the plate. As a vague reference: with a Sylvania or GE sunlamp (275 watt) at 30 inches (75 cm), the normal exposure time is around 6 minutes, but exposure may vary between 3.5 minutes and more than 12 minutes. During the first minute or so, most lamps emit lower amounts of ultraviolet light, a factor that may require an adjustment in the exposure time. A white sheet of paper may be used to judge the UV content. Once the paper appears to acquire violet tint and lose its whiteness, the lamp is functioning in the actinic range. More exposure will bring out more detail in the shadows; less exposure will bring out detail in the highlights. Thus a plate may be etched and re-exposed for a second etching bath to broaden the range of information. Below 3.5 minutes of exposure time with the described light and distance, the resist may not harden enough for an extended developing time. A step scale like Kodak T-14 scale is useful to find out exposure times for a given light. Usability for our purposes starts at Step 4 (out of 14) on the Kodak scale. Step 7 is the step recommended by the manufacturer. On the Stouffer 21-step scale, usability starts around step 5. Keep in mind that playing with exposure means tampering with the information on the transparency. Ideally, each dot on the transparency should have its corresponding open dot on the exposed and developed plate.

Developing

Unlike other liquid photo-resists, where the dye is in the developer or is applied after developing, Ecoresist has the dye built into the resist. This allows for visual control of the developing process. There are two kinds of developer for Ecoresist, a liquid developer and sodium silicate, in powder form. In both cases, developing time is affected by temperature (higher temperatures shorten the developing time). The liquid version of the developer is somewhat quicker than the powder form (time is cut by 30 t0 50%), but bulky for shipping. General handling of the developing process is the same for both developers. Developing can be done under normal light conditions. To make sodium silicate ready for use, one tablespoon of the powder is mixed with one quart (roughly one liter) of distilled water. The water has to be distilled, it cannot be tap water. If the either developer acts too quickly, it may be diluted to 50%.

There are two approaches to developing. One is the procedure recommended by the manufacturer. The plate is submerged in the developer for one to three minutes at 80-90 degrees Fahrenheit (27-31C) while the tray is agitated. Areas being developed have a bluish cast that should be removed as much as possible so that the image is defined by visible metal. The well-exposed resist will be green after the developing process. Particularly stubborn areas can be helped with alcohol. The plate should be rinsed with water, then rinsed with alcohol and rinsed with water again. If needed, the plate can then be put back into the developing tray to continue the process.

The developer may be diluted with up to 50% water, slowing down developing to nearly double the time. When developing this way, a longer developing time is preferable since the margins of tolerance become bigger. The dilution of the developer, however, shortens its shelf life and batches should be prepared according to need. The developer may be reused until it stops working. It can then be boosted with the addition of roughly one teaspoon of sodium carbonate per quart or liter if needed. Sodium carbonate is the main ingredient of water softener powder or soda ash used in washing machines and is available in any supermarket. Proportions need not be precise.

The other approach only differs from the first one in as much as it starts with the developer at room temperature (65F/19C or higher) and the process is aided with a hairdryer. The plate is spot heated with the hair dryer while it is in the developer. The developer should just cover the plate (a 1/8 to a ¼”- ca. 0.5 cm). With the hair dryer on hot and held 2 inches from the plate and while agitating the tray, the image is then systematically heated on the plate until it becomes clearly visible without a bluish cast. Once the image starts becoming visible, it is advisable to interrupt the developing bath and gently rinse the plate, to then return to the developer. This will help seeing the state of the image and prevent overdeveloping. The air of the hairdryer will displace the liquid and possibly even dry the surface for a couple of seconds. The heat seems to activate the developer at the same time it strengthens the exposed photo-resist, protecting it from lifting. The process can take several minutes, from 1 to (rarely) 10 minutes. If the plate is well exposed this extended time will not damage the image. The relative thin layer of developer over the plate minimizes splashing and helps inspection of the plate. It is recommended not to submerge the hairdryer in the developer since it is water-based and therefore the contact may produce a short but unpleasant experience. The developer is reusable until exhaustion, at which point the faint bluish image that initially appears will not change and metal will not become visible even after more than ten minutes passed. Generally the developer remains usable even after the point of looking like a vile purple soup, so judge the plate, not the developer.

After developing, the plate is rinsed well with water and can be dabbed or wiped gently with paper towel and dried with hot air. If during the etch process some areas remain covered by a thin veil that prevents a clean etch, the plate can be redeveloped for a short time and/or wiped with alcohol. The action of the veil sometimes becomes apparent only after the etching bath. In this case alcohol may be poured on the plate and, after rinsing with water, a second developing session may be used. At this point the veiled areas can be gently rubbed with a finger to help the clearing. Alcohol should not be acting on the plate in conjunction with the developer. The combined action of both lifts the coat from the plate.

Removal

As is the case with all photo-resists, the coating of the plate will keep absorbing light and harden after development. Ecoresist seems to harden more than other products we have worked with, and removal already becomes more difficult after 24 hours. An effective removal solution is prepared mixing a sodium carbonate solution, the already mentioned water softener, (two or three teaspoons per quart of water) mixed in equal parts with ethanol alcohol (denaturalized alcohol from the hardware store) and adding a teaspoon of lye (caustic soda in flakes or ready made products like Drano). The soaked resist generally will lift after ½ to 1 hour, but things will go quicker the sooner the plate is cleaned after exposure. If the coat is old, removal may require an overnight bath in the stripper. The cleaning can be helped along with a scrubbing pad used for kitchen pots. Lacquer thinner works as well, but defeat the purpose of non-toxicity of the product.

Re-Exposure

The great advantage of liquid photo-resists is that after etching the plate can be recoated, re-exposed and etched again. The second coat of Ecoresist is applied the same way as the first one. The etched parts sometimes may reject some of the resist. Often etched areas will appear golden and seem uncoated, but usually this is nothing to be alarmed about. However, to allay our fears, the plate can be dried after a first coat and then a second coat can be applied at a right angle. This should be done quickly and without exerting pressure, since the second coat may dissolve the first one and leave brush marks. This will increase the thickness of the resist and require a somewhat longer exposure (from 10 to 20%). However, an etched plate will not have an even color after coating.

The dried photo-resist is abrasion-sensitive. Since jet print transparencies are textured, re-positioning the image on the plate may leave abrasion marks. Therefore it is advisable to use registration marks to control the repositioning and to only gently move the transparency over the image for adjustments. It is always better to re-dry the transparency with a hair dryer before placing it on the plate to avoid its sticking to the plate.

The second exposure time is adjusted for the required information. After developing the exposed plate the same way as the first time, one will expect to see the same even green colored surface. However, as already mentioned, after re-exposure the edges around the previously etched areas still may seem bare. Nevertheless, under normal conditions, the plate is well protected for the etching bath. Abnormal conditions would be an incomplete coating of the plate or bad cleaning and/or degreasing, leading to the lifting of the photo-resist in the developing bath. In this case, one would see the peeling-off marks.

The process of re-exposing is better controlled by using separate transparencies for the needed information for highlights, middle tones and shadows, while maintaining exposure times the same.

Etching

Short etching times are more precise than long ones. Any etchant works both in depth and sideways. After one minute in ferric chloride the dots are much closer to the original size on the transparency than with longer etching times. Therefore, when delicate details are required, it is advisable to etch and recoat and expose several times and to keep the timing to one minute, reaching the final desired depth through several stages of etching.

Storage

The bottle of photo-resist has to be closed extremely tightly to avoid oxidation of the activator component and should be stored in a cool place. Declared shelf life is a year, but in fact should be several years. In hot climates the resist can be kept in a refrigerator. The relatively narrow temperature margins sometimes specified on the label of Ecoresist products (68-80 F or 22-25 C) are for handling.

Safety Instruccions

Ecoresist 60

Work in a well ventilated area. Avoid skin contact with the resist. In case of contact, wash affected area thoroughly with water and soap. Avoid contact with eyes. In case of accidental contact, wash eyes during at least ten minutes. In case of ingestion, rinse mouth, drink water and mineral Vaseline oil (medical grade) and get medical assistance.
 In case of fire, use extinguisher with chemical foam, water spray or CO2. In case of spills, use gloves and remove liquid resist with absorbent materials (paper towel, rags) and wash with water.

Boiling temperature: 119C – 141.5C, flash point ca. 270 C.

Sodium Silicate

Avoid inhalation, ingestion, skin and eye contact. Sodium silicate is neither flammable nor toxic. However, it is an irritant. When spooning the powder, dust clouds should be avoided or a dust mask should be worn. If there is skin contact, wash thoroughly.

Preparation of transparencies with a computer

At Studio Camnitzer we primarily make four-color separation photo-etchings and use Adobe Photoshop to manipulate images and pass them from the RGB mode of the computer monitor to the CMYK (cyan, magenta, yellow, black) mode needed for four-color printing.

For best results the images should have a resolution between 600 and 2100 dpi. Beyond 2100 there seems to be no improvement in the image. The higher the dpi, the more unwieldy the files, so the processing and storage capability of the computer has to be factored in. Once the image looks correct on the screen, it is changed to CMYK mode (image, mode, CMYK in Photoshop). With the channel -window open click on the arrow on the right and go to split channels. This will separate the four colors into separate gray images. At this point the black areas should be checked. A solid black will not accept a pattern that can be etched. Instead it will create an open area on the plate that will have to be aquatinted. In order to accept a pattern, the area that is hoped to print black should only be a dark gray on the image on the screen. By going to image, adjustments, curves, one can measure the output numbers for the different areas. The values that should not change should be locked in on the diagonal line. Then, in the upper levels where blacks are registered, the solid blacks should be adjusted to between 70 and 80%. This will give an appropriate gray to generate a black surface in etching. This percentage may need further adjustments according to the printer being used. Newer printers with more nozzles in the print head may require a lower percentage.

With the channels adjusted for the etching needs, each color will be translated from continuous tones into a mezzotint pattern of black random dots. The reason to use random dots (mezzotint patterns) instead of a mechanical halftone pattern as is customary in books, magazines and newspapers, is twofold. First, the mezzotint pattern blends seamlessly with aquatint techniques often used to subdivide open areas on the plate. Second, the random dots avoid the creation of moiré patterns when printing several plates.

To create a mezzotint pattern with Photoshop, go to IMAGE, MODE and BITMAP. In the window make sure that INPUT and OUTPUT have the same resolution. For METHOD, choose the DIFFUSION DITHER option. The final transparency has to be printed in bitmap, since continuous gray images won’t be correctly registered by the resist. The resist works on a yes-no basis. Either light goes through the transparency and hardens it, or it doesn’t and that area will clear with the developer.

Ecoresist is available from Reprochem S.P.A., 9, Ornago, MI 20060, Italy; tel. +39 039 6286501, e-mail: reprochem (ad) acigraf.com

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Last update July 2012 | Back to top