Viscosity

The viscosity of a fluid is a measure of its resistance to gradual deformation by shear stress or tensile stress. For liquids, it corresponds to the informal concept of "thickness". For example, honey has a much higher viscosity than water.

Viscosity is a property arising from collisions between neighboring particles in a fluid that are moving at different velocities. When the fluid is forced through a tube, the particles which compose the fluid generally move more quickly near the tube's axis and more slowly near its walls: therefore some stress, (such as a pressure difference between the two ends of the tube), is needed to overcome the friction between particle layers to keep the fluid moving. For the same velocity pattern, the stress required is proportional to the fluid's viscosity.

A fluid that has no resistance to shear stress is known as an ideal or inviscid fluid. Zero viscosity is observed only at very low temperatures in superfluids. Otherwise, all fluids have positive viscosity, and are technically said to be viscous or viscid. In common parlance however, a liquid is said to be viscous if its viscosity is substantially greater than that of water; and may be described as mobile if the viscosity is noticeably less than water. A fluid with a relatively high viscosity, for example, pitch, may appear to be a solid.

Viscosity (programming)

In object oriented programming, viscosity refers to the ease at which a developer can add design-preserving code to a system. If it is easier to add a hack than it is to add code that fits into the program's design, then the system has high viscosity. If it is easy to add new code to the program while maintaining the design, then the program has low viscosity.

The name is a metaphor for viscosity in liquids.

See also

Viscosity printing

Viscosity printing is a multi-color printmaking technique that incorporates principles of relief printing and intaglio printing. It was pioneered by Stanley William Hayter.

The process uses the principle of viscosity to print multiple colors of ink from a single plate, rather than relying upon multiple plates for color separation. It is a fine art printmaking technique, making original prints in limited editions, as it is slow and allows too much variation between proofs to make large editions feasible. Color viscosity printing is among the latest developments in intaglio printmaking. Stanley William Hayter developed it during the late 1960s in Paris.

Intaglio

There are a number of different types of original print methods to be aware of. Intaglio prints: for example a dollar bill—bills and most stamps are engraved in metal plates and are printed after a viscous ink (about the consistency of oil paint) is forced into grooves, scratches, etched lines or indentations. The polished surface is then wiped clean using newsprint and tarlatan, leaving ink only below plate level. The plate is then covered with a dampened paper and felt blankets. It is run through the press where great pressure (approximately 8 tons to the square inch) pushes the dampened paper down into the engraved or etched grooves to pick up ink. In other words, in intaglio we see printed what is below the surface of the plate and the ink is now embossed on the paper. Among the greatest masters of engraving and etching are Albrecht Dürer, Hans Holbien, Rembrandt, Goya, and Picasso.