Tuesday, July 7, 2009

Day 2: 1st Etch, Second Etch

Etching: Materials

2 bowls, clean cold water
etching brushes
pH papers
rosin and talc
phosphoric acid
50/50 tapem (tannic acid phosphoric etch mixture) mixture
gum arabic

Quick notes:
*Volume of etch (actual amount of solution applied to an area) affects strength of etch (more volume, stronger etch)
*Talc reduces the surface tension of gum arabic, allowing it to bond more closely with the drawing.

1st Etch

Apply talc carefully and evenly with a brush, polish in with a cotton pad. An uneven coat of talc affects how the etch adheres to the drawing and can cause stray marks in the final image. Rosin is not needed for plate, as it is used mostly as an acid resist for nitric in stone lithography. Plate uses phosphoric acid, rendering the rosin useless.

The pH of gum arabic, straight from the barrel, is about 4.3. The pH of the tapem mixed in the Tamarind recipe is about 2.4/2.3. 

The purpose of the etch is to separate the grease from the pigment of the drawing material and bind the grease to the surface.

Figure the grease content of the image and mix your solution(s) accordingly (every etch is different, and it takes training and practice to identify the proper solution for a drawing, so I won't go into that here) For reference, an etch with a pH lower than 1.5 is technically a counteretch, and will burn off your drawing and reverse the chemistry you are trying to use. 

Apply a mask of gum arabic with a sponge. While the gum is still wet, apply the etch(es) with a brush or sponge, keeping the etch moving but not scrubbing it into the surface of the plate. 2 minutes is a standard baseline for etching, this can be increased if a stronger etch is needed. Exceeding 8 minutes is not a good idea. 

Cool the etch with straight gum and mop up to ensure no etch enters undesired drawing areas. Buff with a cheesecloth. (when you replace the gum film prior to processing, it should be very thin, buffed in very tight. at this stage, a smooth buff with no streaks is adequate. Tamarind processes their plates as early as 30 min. after the first etch, as they tend to use hotter solutions that cause the bulk of the reaction in the first fifteen minutes. There is, however, no harm in letting a plate sit overnight before processing)

Wash out/ Roll Up

A good etch will enable you to wash out the drawing very easily, as it has properly separated the grease from the pigment. To begin, prepare an ink slab and leather roller. The roller should be scraped to remove impurities and old ink. Brace one handle against a solid corner or the roller chock at waist level, brace the other end against your hip. beginning to either side of the seam, but never on the seam itself, flex the knife toward you and start at the bottom pulling upward with minimal pressure. the leather can be bruised or even permanently damaged by this process, so have someone show you before attempting it, as they cost upwards of $300 and you do not want to be responsible for destroying this tool. another note, it takes about 5 months to properly condition a leather roller. don't screw it up. mix up some shop mix and crayon black to get a medium stiff ink. you should work the ink with a knife on the slab for about 5 or 10 minutes, to ensure that all the components are mixed and the ink is workable. use the smallest amount possible. 

Apply a new gum film and buff it down tight. wash out the image with lithotine. it should come right off if the etch was effective. degrease the plate with acetone and a rag. use a cotton pad to check for dirt and oxidation. if further cleaning is needed, lacquer thinner may be applied in the same fashion. do not let solvents dry on the plate- fan to speed evaporation. an interesting note- rag containers that are left open can spontaneously combust- the pressure of the chemical soaked rags stuffed into a can creates heat and can ignite the very flammable rags. always close the containers to prevent oxygen from entering and allowing ignition. 

apply a printing base. tamarind uses a shellac mixture they make themselves that consists on one third shellac, one third alcohol or mineral spirits, one third enamel paint (to tint the mixture and make it easier to see). Pour on a small amount, buff in with a rag. Bake the plate in a plate oven (they use a janky old pizza oven at Tamarind. you can also use a hot plate, heat gun, or hairdryer) at 275 degrees for 5.5 minutes. we were told also that you can use straight shellac, but it must be buffed in immediately before it hardens, and it is difficult to work with in an arid climate like ours. however, it eliminates the need for baking, and once it dries you can proceed directly to the next step. also, it is clear and difficult to see on the plate.

test the shellac with a rag with a little lithotine on it. if no pink color come up on the rag, the plate is ready. apply the asphaltum. less is more, buff it in tight with a rag. let dry. when you are prepared to roll up, wash out the borders, removing the gum arabic with a rag. keep debris out of your sponges. move to the image area and take off as much as you can without scrubbing too much. with one charge of ink on the roller, snap the rest of the asphaltum and shellac off with the roller. keep the stone wet and roll up the image until it is as black as the original drawing. maintain a very fine film of water on the plate, it should look darkened and have a matte finish. 

This is all the notes I took because we got into some very project-specific troubleshooting that has little relevance if you weren't present. However, below are some of the tips I learned.

If an area has come up lighter than you wanted, there are a couple things you can do, before the second etch, to bring it up.

Put a little soft rubbing crayon on a chamois and lightly brush across the light areas. The ink should pick up the rubbing crayon adding a little tone to the area.

You can also dry out the area, keeping other areas wet, then go over the whole plate with a damp sponge and feather in more ink with the roller, concentrating just on the light areas. the lower water content of these areas will attract more ink. 

have fun, you people that are lucky enough to be lithographers. 

These are my original notes from the 2009 Tamarind Aluminum Plate Summer Class, where I'm volunteering as a press assistant. If you have a need, feel free to use these notes. I won't vouch for their accuracy since  I wouldn't presume to know nearly anything about lithography compared to the people at Tamarind, though I do take pretty detailed notes. You should obviously only be doing this is a properly equipped studio with ventilation and adequate tools and supplies. For some serious notes, instructions and formulas, get the book.

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