WHAT IS IT?
| Lithographic printing is used to print the black and white or color photos we see in most magazines, brochures, newspapers, and books. It is also called photo offset printing. |
LITHOGRAPHY: A printing method based on the principle that oil and water do not mix, but remain separate when added together. It was invented in 1798. The 'litho-' part of the word means stone. The '-graph' part means writing. So lithograph means stone writing.
When it was first invented, a greasy crayon made from oil and black pigment was used to draw a picture onto a smooth flat stone. Water was then applied to the stone drawing. The black greasy drawing repelled the water, pushing it away from all the parts of the stone where the crayon was used.
Does this sound like doing a drawing the hard way? It would be,
if the only purpose was to make a single drawing. Here's where the next step of the invention took place. Since the stone was
still wet, any oily black mixture poured over the stone, will still be repelled by the
water. An oily black ink was used for this. When applied to the stone,
this ink remained only on the parts of the stone with the grease crayon drawing.
A blank sheet of paper was then
pressed down onto the stone. When the paper was removed, a copy of the drawing was copied onto the paper. So by adding more water and more oily ink to
the stone, another paper copy was made. This process
was repeated so that many paper copies were made from the single stone drawing. The copies dried and became permanent.
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Did the copy match the original drawing? Not exactly. The drawing was reversed, as if it was held up to a mirror. With current lithographic systems, the final paper print does match the printing master. Why? See Offset-Lithography below. |
How is Lithography used now?
Instead of drawing the original picture, photography is now used in modern photo-lithography.
How is the oil and water principal used with photos?
A printing master* can be made by using photography. This printing master would take the place of the stone. The photographic process can be chemical or electrostatic*. The photo process creates a printing surface where the image is divided up into areas that attract water and repel oil, -or- areas that attract oil and repel water. First water, then an oil based ink is applied to the surface of the printing master. The inked image is then transferred from one surface to another mechanically by bringing the printing master in physical contact with a receiving surface.
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*A
printing master is similar to a printing plate except it is
made of a thin flexible sheet of material. A finished printing master is flat in
appearance. It is flexible so it can be wrapped around a cylinder or drum that
rotates. See the diagram below. |
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| Here is a diagram of a typical offset system | ||||||||||||||
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With this system, the inked image is offset. This means that the inked image from the printing master is transferred first to a rubber covered drum which then comes in contact with blank paper. This go-between step saves wear and tear on the printing master which never directly touches the paper. The image is reversed like a mirror on the rubber drum, but reverses back to normal on the printed paper. The transferred ink portions will produce the printed image. Presses may be designed to handle paper in single sheets or continuous rolls. Paper printed from continuous rolls is cut into sheets after printing. |
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Since there can be only clear paper areas or solid ink areas in a printed copy, how are different shades and colors made in a lithographic picture? |
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Regular Photography is different from lithographic ink printing in one important way when it comes to tones and colors. |
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Photography is a PROPORTIONAL process. It creates different tones and colors on film that match the amount of light and colors in the scene. If magnified, you would see areas of solid color mixtures in the final photograph. |
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Areas of solid color |
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| Lithography is
an ALL or NOTHING process. Wherever
ink touches the blank paper, the ink is applied in a uniform amount. Where there is
image there is ink. So at any point in the printed photo, there is either a full
application of ink, or none at all. |
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Ink or blank paper |
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Since the oil and water principle allows for only two possibilities, areas with ink, and areas without ink, there needed to be a way to print different shades of light and dark, as well as different colors. One answer was to break the picture into very tiny dots. Another answer was to print several color inks on the same piece of paper one on top of the other.
| Making different shades of BLACK & WHITE or COLOR |
A way to break up the inked surface into tiny dots of different sizes was invented. Each dot will print ink as dark as any other, but the size of the dots and the spaces between the dots will make a difference. It will make parts of the picture look lighter, or darker. The dots are too small to be easily noticed. Instead of dots, we see different shades. If you examine a printed photo closely, or use a magnifying glass, you can see the dots. A picture that is broken up into small dots is called a halftone photo or halftone image.
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| In lithography, the ink is the same wherever it is printed. When greatly enlarged, the halftone can be seen as separate dots. It is the amount of white space between the ink that makes a difference. At a normal viewing size and distance, halftone photos appear to be solid tones. |
| CREATING A RANGE OF TONES WITH LITHOGRAPHY | |
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Lithography Halftone |
Magnified halftone photo shows dots |
| What about color? How are dots used to make different colors? | ||||||||
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Color lithography does not need to have a different color ink for every single color in a picture. The color dots allow for several basic colors to appear as a whole range of different colors. When magnified, you can better see the individual dots of color. From a normal distance, the color dots blend visually, and form different color mixtures. A change in the size of the colored dots at any one spot changes the color we see. Usually only four different color inks are used to make thousands of other colors. The process uses the subtractive color mixing system plus black to increase contrast. |
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| Click here for more about COLOR MIXING | ||||||||
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All images are
original artwork or photographs copyright
©1999, 2009 by Robert Truscio |
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PRINTING
MASTER 
