How to Preserve a Rock Fossil With Sealant

Dry the fossil. Water will soften the consolidant, or may harbor bacteria. Owen Green, in his "Manual of Practical Laboratory and Field Techniques in Palaeobiology," recommends baking the fossil in an oven at 85 to 120 degrees F (30 to 50 degrees C) for 12 hours. These temperatures will not harm the fossil; they closely match the conditions found in Africa, Iraq, China or Death Valley--dry places where fossils are typically found.

Mix a consolidant per the manufacturer's instructions. A rock or calcified fossil requires a pure resin consolidant. These are thin solutions of a resin in a solvent like acetone. You brush or dip the fossil, and the solvent evaporates, leaving the resin.
A popular resin consolidant is polyvinyl butyral (PVB, available commercially as Butvar), which is dissolved in acetone. Two other common consolidants are acrylic polymer (available commercially as Paraloid B-72) and polyvinyl acetate (which is found in Elmer's Glue). Paraloid is gaining ground in lab use, as it dries very hard; and it is popular in the conservation of art and books, so is quite suitable to harder objects like fossils.

Brush or airbrush the fossil with consolidant until it ceases to penetrate the fossil. This means that the consolidant has filled all the cavities, cracks and fissures.

Dip the fossil, as an alternative. This is a faster method, but uses more of the costly consolidant. Allow the fossil to dry before mounting or otherwise preparing it.