Both technologies use polarized particles in goo. In eInk's case, the particles and goo are encapsulated in tiny gelatin capsules-using the same mature technology that the pharmaceutical industry uses to produce time-release medications. The means that the material is, in many senses, an ink. It can be used in suitable pens or printers. ''In many ways it is like conventional toner technology,'' eInk's senior marketing manager Darren Bischoff said.

Once the capsules have been deposited on their substrate — plastic, or even actual paper-applying an electric field orients the electrophoretic particles inside the capsules, and thus changes the reflectivity of the surface of the substrate.

At the current state of the technology, maximum contrast is about 8-to-1 or maybe 10-to-1. ''This is still considerably better than the 6-to-1 people are used to from a newspaper,'' Bischoff observed. Maximum resolution now is about 170 pixels per inch.

Data retention is a more divisive issue. Palo Alto Research Center member of research staff Raj Apte estimated that electrophoretic materials like those from eInk had to be subjected to a refreshing field every few minutes to every few hours in order to maintain contrast. Bischoff disputed this, saying that eInk had samples that had remained legible for months, and could have possibly remained so for years. ''Memory depends on a number of variables, including how the material was driven in the first place and the environment it is in,'' Bischoff said.

Unlike eInk, which in effect makes ink, Gyricon makes sheets of material that ''resemble a thick, robust sheet of viewgraph film,'' according to PARC's area manager Eric Shroder. The material, according to the company's Web site, is a sandwich that seals the black-and-white polarized particles into tiny compartments formed between two thin plastic sheets. Shroder described the contrast ratio of the material as ''around 10-to-1-more like a reflective LCD than like good printing on a sheet of high-quality paper.''

It was not clear what the maximum resolution of the Gyricon material is today, but PARC's Apte suggested that one could expect something in the range of 75 dots-per-inch from the materials. The material appears to have a very strong memory effect, retaining an image that is nearly permanent unless it is disturbed by outside effects-such as a spark from the finger of a statically-charged user.