[drcy]

In general, for best color lithography (T206s, Topps, Bowman, T3s, etc) you want a white background (glossy smooth is nice not but required) and for the best monotone photoengraving (1910s Sporting News inserts, others) you want super smooth (which translates to glossy). You can print photoengraving on matte paper (see old newspapers and magazines) but it won't be as sharp-- and, in fact, early 1900s newspaper pictures are pretty crude. If the Sporing News were color photoengravings, they'd probably be on white stock.

The printers picked the stock they wanted beforehand and for super glossy front cards such as the Sporting News inserts, they chose a glossy front stock. Notice with the Sporting News inserts that only the fronts are glossy, and with the T206s only front has the white coating. That's because the player pictures are only on the fronts and the backs are just text.

The gloss or lack there of was added during manufacture of the cardstock or paper itself, not during or after printing. The printers picked the stock based on the type of printing they were using and the desired quality of the final product. You would want a newspaper's premium on 'fancier' stock and probably with better quality graphics than the daily newspaper. And notice that the picture sections of many many books are on whiter, smoother paper than the rest of the book.

As already noted, real photo cards have a transparent coating to hold the photochemicals to the paper, and that gives the fronts a typical gloss. Again, the coating was added during the manufacture of the paper.

As far as authenticating and fake detecting baseball cards, correct gloss is one of the hardest things to duplicate. Nearly all counterfeits and reprints have a different gloss than the genuine cards. Even Topps' reprints of their own cards have different glosses.

And, in fact, there is a small scientific instrument called the glossmeter that measures gloss. Put it in on the surface of something and it gives a numerical reading. The inside of the instrument shines a beam of light off the surface and measures how much is reflected off. A mirror, which is designed to reflect back a clear image, measures at 99.9 percent glossy-- the highest reading the glossmeter will give. The glossmeter is usually used for quality control by paint manufacturers, but can be used as easily on trading cards.