A) Screen Printing:
Screen printing uses a water like gelling agent with ink mixed in. A screen or stencil is placed over the bag and the ink is applied in the desired colours. The screen is then removed and the bag is left to dry. Since screen printing does not involve chemical solvents, the screen stencil can be washed with just water. The advantages of this printing technique are the image can be in almost any colour, it is long lasting, water resistant, odourless and works well on many materials. The disadvantage is that as this method is usually done by hand, for multicolour printing, the positioning may not be accurate which can create smudged or distorted images. As well only solid colours can be screen printed, you cannot show gradations or shading with screen printing.
B) Offset Printing:
is a commonly used printing technique in which 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 image carrier on which the image to be printed obtains ink from ink rollers, while the non-printing area attracts a water based film, keeping the non-printing areas ink-free.
C) Foil or Stamp:
is the application of pigment or metallic foil to paper where a heated stamp is pressed onto the foil, making it adhere to the surface leaving the design of the stamp on the paper. Foil stamping can be combined with embossing to create a more striking 3D image.