Methyl Cellulose is an acid-free adhesive, often used for bookbinding and paper repair. By itself it is a relatively weak adhesive. However, when added to PVA glues, it extend the drying time and allows the glue to be spread easier. By extending the drying time it also enables repositioning of the glued paper or bookcloth.  Comes in powder a form. Mix one pint  warm (or room temperature ) water to 1 or 2 tablespoons of powder, depending on desired viscosity.  After mixing with water, this product has a 6 month shelf life as long as it's kept in a covered container.