*Clean the material: The very strongest glues are made with un-decayed and thoroughly cleaned materials. Fats, muscles, dirt and other non-collagen materials are removed as much as possible before the material is boiled. This can be accomplished by liming, or soaking in wood ashes, followed by thorough, repeated scraping and washing to remove dissolved solids and residual lime. However, very strong glue can be made by boiling fairly clean materials like sinew and even skin from lean animals without undergoing so thorough a treatment. At the very least though, skin should be very thoroughly fleshed and washed.