Bill Houghton, Sebastopol, CA
From the 1907 Popular Mechanics "Shopnotes:"
"TO MEND AN OLD SHINGLE ROOF
"Cut pieces of tin about 7 in. by 2 in. from old cans that are not too rusty and slip these under the joints and cracks in the shingles....In this way, an old roof can be made to last several years."
Speculation remains open as to how long it would last if you used tin that was shiny, or, at the other extreme, too rusty.