Must be in the form or consistency of medium stiff putty and the following makes the best composition, which should be run through a water cooled mill with large eye; taking good care not to overheat the material:
60 pounds basic carbonate of lead, dry;
fine bolted whiting;
rubbing varnish of high grade;
raw linseed oil;
A thin coating of this compound is applied, when the sheets are rivetted together, the excess being pressed out during the operation, and collected for future use.