By Eileen M. Foti
One of the questions most frequently asked by artists who
are beginning to work in lithography is why their counteretching attempts fail.
They find that the newly drawn areas do not roll up, they roll up in an
inconsistent fashion, or they eventually begin to fade during printing. There
are a number of reasons why these problems arise. Below is a detailed list of
possible counteretch mixtures for stones and aluminum plates and a step-by-step
guide to the process.
Counteretch solution is used to remove the adsorbed gum
film created by the first etch on the plate or stone’s negative areas. In
order for that element to again become grease-receptive so as to accommodate new
drawing, this layer must be completely removed. It is critical to do a thorough
job, or else overlooked traces of that gum film will affect the establishment of
the newly-drawn areas.
When choosing a counteretch formula, one should always opt
for the least corrosive formula, so as not to damage the grain of the stone or
the plate. Make sure to follow the directions given below, and remember that
each time a plate is counteretched, its grain is compromised. Consider all areas
that need to be counteretched and do them at the same time, therefore minimizing
the number of times that the plate will need this process.
Counteretch
formulas for stone are:
Used primarily for stones, this mild solution will not
damage the surface grain. It should be mixed as needed and not stored for more
than a day. Its effectiveness in removing gum will be increased by using warm
water.
1/4 teaspoon monohydrate citric acid crystals
10 oz (300 ml) warm water
Acetic
acid
This acid is much more corrosive than citric, and therefore
is not recommended for use as a trustworthy counteretch. Instead, it is very
useful for removing a "ghost image" on a stone during the graining
process. If the previous image is stubborn and hard to remove while still
graining at the lower numbers, one can pour this mixture onto the stone and let
it sit for two minutes. Rinse thoroughly with water, and then keep graining.
1 part glacial acetic acid
10 parts water
Counteretch
formulas for aluminum plates are:
Phosphoric/Hydrochloric
This is the most dependable counteretch for aluminum.
However, as with all counteretches, it must be used correctly so as not to
damage the grain.
1 oz (30 ml) phosphoric acid
1
oz (30 ml) hydrochloric acid
1 gal (3490 ml) water
Hydrofluoric
acid
This type of acid is not only highly corrosive to plates,
but it is extremely dangerous to people. Its vapors will cause severe irritation
to the upper respiratory tract, and serious burns will result from contact with
skin. This counteretch is not recommended, but if one must use it, then
gloves, eye protection and a respirator or strong local ventilation is
absolutely necessary.
1 oz (30 ml) hydrofluoric acid
1 oz (30 ml) ammonium alum
1 gal (3490 ml) water
Mixing and applying a counteretch solution
Handle acid in a well-ventilated place, wearing gloves and eye protection. If skin comes in contact with acid, wash immediately with water. If eyes come in contact with acid, call for help and flood eyes with water for at least fifteen minutes. When mixing the solution, pour the acid into a glass measuring cup, situated safely back from the counte’s edge (use plastic if pouring hydrofluoric, as it reacts to glass). Always pour acid into water, as the reverse could cause a cloud of dangerous fumes to immediately bubble up. After mixing, wash all utensils under running water. If acid spills, then neutralize the area immediately with baking soda or magnesium carbonate as an absorbent.