Commonly called optical cards, they were manufactured by Landis & Gyr in Switzerland, Great Britain, and Taiwan. The reading was carried out by the telephone set using a laser beam that reflects a slight incision on a thin aluminum band on the board. The shots were then deleted by a thermal system that physically destroys the relief of the part used and allows you to see the amount of shots taken. The first cards did not have the classic white band, so to know if the card is used or not you have to keep it with a certain inclination to the light, so that the notches produced by the thermal system are visible. To avoid this problem, after a certain period the cards were manufactured with a thermographic band superimposed on the aluminum reading band; on this band, white, the thermal system caused a small burn that, in the form of a black bar, allowed to easily see the actual use of the card.
Therefore the optical band is only the metal strip that crosses the card at about 15 mm. from the top edge, and the initial and terminal parts can be seen on the edges of the card. The white band of thermographic paint that covers the optic one has had different heights over the years – 1.5 mm, 2 mm, 4 mm and finally 3 mm – and similar cards but with bands of different heights can have very different ratings. On the most recent cards the white band has been eliminated in order to favor the graphics: therefore the front side of the cards is completely covered by the image, and, thanks to an innovative technique, the actual use of the card can be viewed on the back. Until 1988, a printing technique was used for which the cards appear covered with a kind of paint, and generally they are of a single color on a silver background; but from 1988 onwards they started to use offset printing, and from 1991 all the cards were printed with this technique.
A serial number is usually stamped on the back of the card, through which you can often know the year of production. In fact, the initial figure represents the year and the two following the month in which the card was produced. For example, 306H … means that the card was produced in 1993, June (06). The only problem is that there are no apparent differences in the serial number between a card manufactured in 1988 and one in 1998, but it is sufficient to see the type of print, to be able to easily distinguish between them.
