In 1939 the Union Oil Co. of California began publishing postcard views of Southwestern scenes which were given away as premiums in the company's service stations. The Union Oil cards introduced new printing technology. Cards were printed in four-color half-tone process with a varnish overcoat called photochrome probably because of their link to Kodak's newly introduced Kodachrome color reversal slide film. Kodachrome slides were the cornerstone for most of these new photochrome cards. This name soon was shortened by collectors to chrome. This new technology yielded a high-quality, detailed image with a shiny surface that was close to photographic quality and in realistic color. World War II slowed their spread but in the early 1950's chrome cards took over the postcard market replacing both linens and black-and-white real-photo views.

Postcards to this day are still almost entirely chromes. The computer has changed the look of view cards in the last few years as designers working with digital image-editing software have turned blue skies into blazing sunsets with expanse of color not seen since the linen cards of the 1930s. In addition they added larger and larger type effects reflecting the public's preoccupation with logos and brand names.

The most noticeable change in postcards since the beginning of the chrome era has been their size:

- "Standard." For almost a century the standard size for a postcard was 5 1/2 inches by 3 1/2 inches. The first postal cards issued by the Post Office were roughly the same size as a standard mailing envelope in the middle of the 19th Century. Private manufacturers of postcards quickly began to experiment with the size of cards -- small ones and fold-outs and double-wide panoramas for example. Throughout the golden age of postcards though from the pioneer era through white borders and real-photos and linens and chromes, the vast majority of postcards were this standard 5 1/2-by-3 1/2 size.

- "Continental." In the last two or three decades it seems everything in America has been supersized, from french fries to toilet paper. Postcards are no exception. The "standard" size for postcards has increased from 5 1/2-by-3 12 to 4-by-6. Collectors call these larger cards "continentals," because presumably the larger size first became common on the Continent.

- "Supercontinental." The latest development in the never-ending battle to create something that will catch the public's eye and pry open its wallet are postcards that are even larger than "continental" -- 7 by 4.5 inches and up. These are too big to mail at the postcard rate (currently 23 cents): the Postal Service requires letter-rate postage, 37 cents. Probably few of them are actually mailed, anyway. These megacards seem to be marketed as souvenirs, mini-posters to be taken home and put on a mirror or a refrigerator for your own enjoyment or memories.