SAN FRANCISCO— Although digital typesetting and offset lithography have largely rendered type casting obsolete, letterpress printing and type founding remains alive at Grabhorn with techniques and equipment a century old. One of perhaps 100 people worldwide who cast type.  By the 1980s, nearly all letterpress gear was abandoned when offset printing took over. Grabhorn’s Institute has  kept the tradition alive with art prints, small editions of books, wedding invitations, and posters.The type is sold by the pound to letterpress printers. With letterpress printing, letters and images stand in relief.  More crucially, the type casts is used to print limited-edition books in the Grabhorn Institute’s adjacent pressroom on letterpress equipment of a similar vintage. Sold for hundreds to thousands of dollars each, these books form the largest part of the institute’s revenue and sustain it for the future.