Sometimes (and not so infrequently), you have films that, either due to exposure errors, or because they are used and developed decades after their expiration, are underexposed (ie too dark). From today it is possible to solve this problem: 
 In fact, the film lightening service is available  black and white positive.
 You can also get exposure values of +4 stops, saving useless films.
 The film will be legible e  well projectable.
 The treatable films are:
 Kodachrome 2, Kodachrome 25, Kodachrome 40, Kodak tri-x, Adox pan X reverso, Kodak plus X, Kodak Double X, Agfa Scala.