of sorts of lithographic stones. (source:
stones have a close and compact, yet porous structure. They
should be handled with care, because they are very hard and
brittle; when they break, they part cleanly with a
conchoidal fracture. Stones must have a certain thickness ,
depending on over-all size, to withstand the pressures of
the printing press without breaking.
The color of a stone
indicates its hardness and quality. The following seven
grades of color are recognized for lithographic
- Blue stones.
These are the most ancient, most compact, and darkest of
all the lithographic stones. They were subjected to the
greatest pressures and heaviest infusions of mineral
pigmentation during their formation. Being denser, purer,
and rarer than other grades, these stones were in the
past highly prized for engraving purposes. They are
generally too dark for artists' drawings and are too
heavy for general lithographic use today.
- Dark gray
stones.These stones also are rare; they are somewhat
lighter in color than blue stones, but usually too dark
for the artist to develop tonal gradiations with ease.
They are excellent stones for engraving, for solids, and
for linear work.
- Medium gray
stones.These are the most desirable stones for use in
lithography. The tonal range of a drawing can be clearly
seen. Though less hard than the previous categories,
these stones are of ample density to withstand strong
lithographic etches enely and without coarsening. Today,
stones of this quality are rare (particularly in large
sizes) and are highly prized. They make possible the
printing of very large editions with remarkable
- Light grey
stones.These stones are a light, cool grey. They are
the youngest and softest of the limestones in the gray
category. These are found in greater numbers than the
medium gray stones and can be used with excellent results
for all varieties of work. Occasionally, marine fossils
are found imbedded in stones of this color.
- Hard yellow
stonesThese stones have a warm tan color. They are
less dense than the grey varieties, although they are
still capable of producing a satisfactory range of work.
Most of the large stones brought to the USA were of this
quality. Being relatively soft, stones of this quality
cannot withstand strong etches without some coarsening.
In addition, the sharp granularity that is characteristic
of grey stones cannot be produced on hard yellow stones;
crayon drawings with fine tones and delicate tusche
washes executed on such stones therefore appear somewhat
- Soft Yellow
stones.These stones are lighter in color and even
softer than the previous category. They usually have an
uneven density and are composed of greater percentages of
silica, ferrous oxide, and other impurities. Some of
these impurities will resist the action of the etch more
than others, thus roughening the surface of the stone and
undermining parts of the image. Soft yellow stones are
suitable only for the coarsest type of drawings and are
not recommended for processes that require extensive
corrective procedures. Linear work and autographic
tranfers print fairly well from soft yellow
stones.These are the most recently formed, the
softest, and the least desirable of all the grades of
lithographic stone. They are chalky white and invariably
contain large percentages of impurities. White stones are
generally incapable of producing dependable results for
any type of lithographic use. They are used only because
of the general shortage of all grades of stone, and only
for the simplest types of printing.
In addition to color,
lithography stones display other physical characteristics
that govern their quality and performance:
Iron marks These may
appear on the surface of the stone as bands, ribbons, or
streaks of dark grey, bluish grey, or pale reddish brown.
They result from iron oxides in differing states of
oxidation reduction which were present during the formation
of the stone. Though sometimes visually distracting, they
seldom interfere with the lithographic properties of the