Behind the Scenes at NYPL's Conservation Lab 

Conservators perform a technique called "spot testing" which is using a solvent (water, acetone, ethanol, etc.) on an inconspicous area of an original document to see how the media/paper will interact with it. They usually start from the weakest to strongest solvents. However, it doesn't ensure the paper won't react differently when it is treated with larger amounts of the solvent. Testing on other documents would help to see how the solvents could react, but it wouldn't help as far as testing for a specific document because more than likely, the paper type and media of the original is completely different from the others. There's so many layers to it!

Japanese paper or Kozo paper is see through, and either way the mat will be covering it when back for display and conservation is complete.

Late reply. Generally they lightly brush it with a goat hair brush to remove any loose surface dirt. Compressed air is also used.

Cuando trabjas en este campo siempre te limpias la anos antes, durante y despues de tocar un documento. Algunos docuemntos como los que se han presentado en el video no estaban en un estado de deterioro extremo y podían manipularse con facilidad, por eso seguramente no utilicen protección para moverlos o tocarlos. (Te lo digo por experiencia)