back to Technical Talk

PRINTING BASES FOR ALUMINUM PLATE LITHOGRAPHY

The introduction of the offset press and aluminum plates to commercial printing resulted from the need to create printed matter at a faster pace. The offset machine replaced the hand-operated press that once printed images from stone. With materials from the offset industry readily available, the quality of printing from plates in hand lithography has greatly improved. This article addresses the effectiveness and safety of lacquer and shellac as printing bases in hand lithography. Lacquer and shellac are the two most commonly used printing bases today. In the past, products such as Titan vinyl lacquer and Blue C Lacquer were used frequently despite their highly toxic nature. The somewhat less toxic Lacquer V (made by Hanco) is today's printing base of choice, although it dries slower and is less durable than the others and is more toxic than the alternative materials described below.

A decade ago, Tamarind's former education director, Jeffrey Sippel, refined a shellac alternative to the widely used lacquer base. While teaching in Poland, he noticed that printers there were using shellac as a printing base. The problems they encountered seemed to be related more to the application of the material than to the material itself. The uneven film, caused by the rapid drying of the shellac, compromised the quality of the image and edition. Jeff's previous experiments with oil paint as a printing base had been problematic because the oil paint dried too slowly. His solution was to combine materials-1/3 shellac (make sure it is high quality shellac, one that has no water in the contents), 1/3 oil-based enamel, and 1/3 mineral spirits--to come up with a solution that worked well. In fact, Tamarind printers still use it today.

The advantages of shellac are:
1) vapors are less toxic;
2) acetone (used to wash out shellac) is safer than Hancolite (used to remove lacquer);
3) shellac is more easily removed from the matrix, which helps to prevent the image from "filling in" or from getting darker during the roll-up of an image.

The disadvantages of shellac are:
1) if an image in a shellac printing base is not baked long enough, it is susceptible to "water burn" or "dropping out" (gradual fading of image);
2) the shelf life of shellac is short (only a few months);
3) pre-made shellac separates if not thoroughly mixed and must be stirred well before use.

The advantages of lacquer are:
1) once lacquer is cured (we use a hairdryer), the printing base creates a film that is resistant to problems associated with shellac;
2) the image is more durable;
3) it dries quickly;
4) shelf life is many years.

The disadvantages of lacquer are:
1) it can irritate skin and mucous membrane, and can cause headaches and fatigue;
2) long-term use can be harmful to the respiratory system. The use of a respiratory mask or proper ventilation may alleviate these effects to some degree.

More and more printers prefer to use safer materials, especially in classroom settings. The shellac mixture may be the best alternative, although the curing method could be problematic for many facilities because it is ideal to use an oven for curing the image. Alternatives to baking the plate in a special oven are discussed below.

Shellac method as used at Tamarind
1) Mix base in the following proportions: 1/3 shellac*, 1/3 oil-based enamel, 1/3 mineral spirits.
2) Etch image, let rest for a minimum of 1 hour. Wash out image first with lithotine, then with acetone. The acetone will remove any residual drawing materials still left on the plate.
3) Stir shellac mixture well, then apply with a clean rag.
4) Buff well with a clean rag.
5) Heat in a custom made oven at 250 degrees for 10-15 minutes. Shorter heating time can cause problems during proofing and/or editioning. Heating the shellac causes the printing base to adhere better to the surface of the plate and thus creates a stronger and more stable film that cannot be dissolved with lithotine or isopar.
6) Remove plate carefully (it's hot!).
7) Apply asphaltum and buff. Roll up as usual.

The following methods do not require an oven.

A. Buffing shellac mixture
1) Etch drawing, let rest for miminum of one hour.
2) Apply a new gum mask to the image, wash out with lithotine and then acetone.
3) Buff in a small amount of the shellac mixture (1/3 shellac, 1/3 oil-based enamel paint, 1/3 mineral spirits) well, until no traces of shellac are visible on a clean rag.
4) Fan the plate dry for two minutes.
5) Buff in alphaltum, wash out with water, and then roll up with black ink.
*The plate was stored for a few days and then printed in an edition of fifty impressions. There was a visible change--a lightening of the crayon drawn areas--after 35 impressions The tusche washes (Stones paste tusche), remained consistent throughout the edition.

B. Elimination of mineral spirits from mixture
1) Follow steps 1 and 2 above
2) Mix thoroughly: 1 part shellac (use good quality clear shellac) and 1 part oil paint enamel; stir well.
3) Apply the mixture immediately and buff into the plate. Rapid drying causes an uneven film on the plate, so be sure that the entire image is coated.
4) Fan the plate dry for two minutes. Buff in asphaltum, and then roll the plate up in black ink.
5) Wash off the asphaltum with water; there should be no visible sign of the red oil based enamel pigment.
*The crayon and the tusche drawn areas printed consistently. There was no visible change in the edition of 50 impressions.

C: Use of clear shellac only
1) Apply shellac quickly and evenly. It will dry as soon as it touches the plate, which makes it difficult to apply an even film. The plate will show a very slight color change where the shellac has been applied.
2) Process the plate as indicated above.
*There was a slight change (gradual lightening) of the darkest areas, but the changes were not as dramatic as those with the shellac mixture in A. The tusche washes printed consistently.

Conclusion
The mixtures used in B (1 part shellac to 1 part oil-based enamel) and C (clear shellac) above are fairly reliable and stable for editioning. Since the average edition size in a university setting is normally under 25 impressions, any of these shellac combinations should be satisfactory printing bases for aluminum plate lithography. It is difficult to say which is better, although for printing long editions Hanco's Lacquer V is more durable and reliable. Safety is an important consideration in choosing materials.

We welcome your questions and comments: tamarind@unm.edu
All contents ©1998 Tamarind Institute All rights reserved.
Web site maintenance by Marjorie Devon, tamarind@unm.edu
http://www.unm.edu/~tamarind/techtalk.html
Last updated: January 30, 2001.