Near the beginning of Indiana Jones and the Last Crusade, after copying the rest of the missing inscription from the knight's tablet onto what appears to be some kind of rice paper, Indiana Jones and his lady assisistant swim under a burning river of petroleum to escape.
Is there a real type of paper with the properties of the paper in the film that could survive such a dunk?
The script does not specify what sort of paper is used, but I always assumed it to just be a regular piece of tracing paper.
Tracing paper is a type of translucent paper. It is made by immersing uncut and unloaded paper of good quality in sulfuric acid for a few seconds. The acid converts some of the cellulose into amyloid form having a gelatinous and impermeable character. When the treated paper is thoroughly washed and dried, the resultant product is much stronger than the original paper. Tracing paper is resistant to oil, grease and to a large extent impervious to water and gas.
But historically, most rubbings are done with a paper that is very similar to Butcher paper which is also very resistant to water.
Interestingly, the script makes specific mention of the rubbing being "soaked", though it does not indicate that it is damaged at all.
CLOSE ON THE WATER-SOAKED PAPER IMPRESSION: The rubbing taken from the shield of the Grail Knight.
The film's official novelisation makes it clear that it's just "paper", rather than tracing paper, butcher paper, Kraft paper or any other kind of specialist parchment.
As to its condition, Indy is pleasantly surprised to see that it's held up so well after its immersion. Note that it's been carefully dried.
“Better, now that I’ve seen this. It finally dried. You’ve got to take a look.” In spite of the ice pack, Brody sounded as excited as Indy had ever seen him. He hurried into the library and dropped the piece of paper on the massive mahogany table that dominated the room. The paper was what remained of the rubbing from the knight’s shield. It was smeared and faded from the soaking in the tunnel, but was still in one piece. Now that it was dry, Indy could see that it was fairly legible.
