CONSERVATION: DOUBLE FOLD TEST
The double fold test is used to test paper for embrittlement. The normal rating runs from 0 to 5 double folds, 0 being the most brittle 5, the least. Even though paper may survive five double folds without breaking, that does not mean the paper is not acidic. It only means that the paper has not yet reached the stage of embrittlement to which we need to replace or reformat. Further information on embrittlement and/or reformatting may be obtained on the Reprographics pages.
These guidelines apply to all types of bound materials and all styles of binding. Items considered rare or unique should be excluded from these guidelines and routed to the Conservation Unit.
To use the double fold test (DFT) , perform the following steps:
- Open the book to be tested near the center and pick a page at random.
- Lift the bottom right corner of a single page.
- Fold over a small corner, 1 cm or less, and crease lightly.
- Fold corner all the way over in the opposite direction and crease again.
- If the paper breaks at this point, it is 0 DFT.
- Straighten the corner back up.
- Grasp the corner between the thumb and forefinger and tug the flap straight up.
- If the paper breaks at this point it is 1 DFT.
- Repeat the above until the paper breaks or it has been repeated five times.