Ferber is coy about the composition of the inks but said T-Ink has moved beyond the materials used to make traditional conductive ink — particles of silver and carbon. T-Ink's patent applications describe using various mineral powders and some conductive plastics. The inks can come in any color and can be washable, too.

For all of Ferber's enthusiasm, conductive inks have drawbacks. Blue Ramsey, a researcher at Brunel University in England, has studied high-speed printing and points out that for one, conductive ink has more resistance than the copper used in traditional circuit boards. That means it can't carry a strong current efficiently.

Also, ink isn't very practical for making circuits that can do something smart, like performing a calculation. It isn't yet possible to print circuits that are as dense as those in a silicon chip, so a printed calculator would have to be huge, probably several square feet.

"You need a fairly large area to do anything clever," Ramsey said.

Also, engineers have had trouble making a magnetic ink that is strong enough for a loudspeaker, meaning Ferber's goal of a talking newspaper is at least several years away.

T-Ink is close to printing batteries, Ferber said, but for now, his designers have to connect ink circuits to batteries, chips and speakers made with more traditional technology.

Still, there's plenty that can be done with simple conductive ink, and the field has attracted competitors, including Flint Ink Corp., the world's second-largest maker of inks.

"Printing conductive inks using high-speed printing processes would provide for huge cost savings," says Jim Rohrkemper at the Ann Arbor, Mich. company.

Flint Ink, which has 5,000 employees, has set up a unit to develop methods of cheaply printing antennas for radio-frequency identification tags, the tiny chips that retailers are hoping will replace bar codes.

Widespread adoption of RFID tags is being delayed by cost. Though much of it is due to the chip, which can't be printed, printing the antenna part could help bring the total price down.

Others in the field include Power Paper, an Israeli company that prints paper-thin batteries used by Hasbro in stickers that play music when pressed. Those batteries plus electronics cost 20 cents to a dollar to make, too much for many applications. T-Ink believes it can undercut that price substantially.

Several companies, like Seiko Epson of Japan and E Ink Corp. of Cambridge, Mass., are working on printing bendable computer displays on paper — essentially computer monitors that you can roll up and fit in your pocket.

No one is trying to take the concept as far as T-Ink, however. It is even working on conductive ink that can be added to candy. The idea is to give pieces of candy differing electrical resistance, so an electronic game board can recognize them as different playing pieces. Presumably, the winner gets to eat the pieces.