But copying old films to new stocks is not as simple as it sounds. There are many factors that can impact your ability to be able to do that very well, especially with nitrate archival films. Shrinkage is the most notable. Original era nitrate negatives were showing significant shrinkage shortly after they were shot and processed. After it was developed, the film had to be dried again, so that it didn’t stick to itself, and one of the plasticizers used to keep the film flexible was quite volatile, and could shrink considerably. In some cases, you can actually see the perforation from the original negative printed onto the original positive.
Other challenges come from running a fairly soft material — the nitrate film — through pieces of steel, the projectors, and the sprockets. If things weren’t running quite perfectly, bases and emulsions got scratched. Static electricity attracted dirt to the surface, where it could be embedded in the emulsion.
All of these problems can show up on new prints, so we have various pieces of equipment designed to help us overcome those.
The introduction of wet gate printers, or immersion printers, was the sea change in the world of preservation. They allowed laboratories to make fairly pristine copies from films that were otherwise horribly scratched, by immersing the film in a liquid — perchloroethylene, the same fluid used in dry cleaning — to fill in the scratches.