1902 Keystone View Company Antique Stereoview Image Card: 1,991 ppm Lead + 204 ppm Arsenic.

From the following website (link):

“The Keystone View Company was founded in 1892 by B. L. Singley in Meadville, Pennsylvania. This might not sound like an auspicious location, far from the photographic centers of New York, Boston, and Philadelphia, and originally the operation did indeed have a “backwoods,” quality, turning out distinctly second-rate stereoviews and barely making the founder a living. But it rapidly improved and eventually became not only the world’s largest but also the best view company. In the formative days Singley took all the images; later there were dozens of staff photographers. Equally importantly, in the early 1900s, when stereoviewing was declining and other companies were in trouble, Keystone bought their stocks and incorporated them into their own holdings. Notable amongst many such purchases were the huge and varied inventories of B. W. Kilburn, the H. C. White Company, Underwood & Underwood. As a result, Keystone was said to have had some 2 million negatives by the mid-1930’s. While this is likely a wild exaggeration they did have about 50,000 numbered views available. They developed the technique of consistently producing beautifully clear, crisp prints which were a delight to view; originally they were mounted on tan curved cards and later on their trade-mark dark gray curved mounts. The company also emphasized the use of informative text on the back of the views, and popularized the concept of boxed sets which had been innovated by the Underwood Brothers.”

When tested with an XRF Instrument the view card (from 1902) pictured here had the following readings: