Screen Printing
A screen is made of a piece of porous, finely woven fabric
(originally
silk, but typically made of polyester or nylon) stretched over an
aluminum frame. Areas of the screen are blocked off with a
non-permeable material—a stencil—which is a
positive of the
image to be printed; that is, the open spaces are where the ink will
appear.
The screen is placed on top of the disc. Ink is placed on top
of the screen, and a rubber blade(squeegee) is used to push the ink
evenly into the screen openings and onto the disc. The ink passes
through the open spaces in the screen onto disc below; the screen is
lifted away and then the squeegee is pushed back across the screen,
with the screen lifted, "flooding" the ink into the screen. The screen
can be re-used after cleaning. If more than one colour is being printed
on the same surface, the ink is allowed to dry and then the process is
repeated with another screen and different colour of ink.
The vast majority of silk-screen printings are used for a
design without full colour.
Litho Printing
Litho printing is a widely used printing technique where the
inked image is transferred (or "offset") from a plate to a rubber
blanket, then to the printing surface. When used in combination with
the lithographic process, which is based on the repulsion of oil and
water, the offset technique employs a flat (planographic) image carrier
on which the image to be printed obtains ink from ink rollers, while
the non-printing area attracts a film of water, keeping the
non-printing areas ink-free.
Offset printing is mainly used for more complicated designs
where the images need to be very clearly defined, the advantage of
offset printing is that the different images in the design will be
separated and not run together.