Perforation repair tapes are available commercially and the time saved by not having to cut the tape away from the perforations is worth the expense of the tape. Again the issue of shrinkage appears. Perforation repair tape is designed for unshrunken film. However, if it is used to cover no more than four perforations at a time then the effect of the difference in shrinkage is usually marginal. All that is required is care in aligning the perforations in the tape with those on the film.
If the film surrounding perforations is significantly damaged or missing altogether then a technique called 'bridging’ is useful. The bridging technique attaches a different piece of film, with identical shrinkage, to replace the original perforations.
- Clean up the edge of the film by removing any odd pieces of film that may catch during transport (Fig 11.5 i).
- Select a suitable piece of scrap film ensure that the shrinkage is nearly identical (Fig 11.5 ii) and trim it so that there are two or three perforations extra at each end. Cut this film down the centre line. This gives a nice handle to work with while you are aligning and cementing the bridge.
- Clean the emulsion off the repair piece and gently scrape the ends of the film where the bridge is to be attached. Align and overlap with the perforation at each end of the repair and cement the new section (Fig 11.5 iii).
- Finally, trim the handle away using a sharp scalpel and a straight edge (Fig 11.5 iv).
There is no need to cement down the centre parts of this repair unless it runs for several frames. If this is the case then a drop of cement every two or three frames is sufficient.