@albada, this is a simplification that is not entirely reliable. While the present C41 does indeed include a
final rinse, this final rinse serves a couple of purposes:
* Removal/dilution of traces of fixer
* Addition of a fungicide to the emulsion to prevent deterioration of the emulsion itself in later life
* Actual stabilization of the color dyes
* The final rinse generally contains a wetting agent that helps to prevent drying marks
The relevance of most of the above depends on several other factors such as processing context/equipment and film storage. But the stabilization of the dyes is necessary for older films up to 20-30 ago (see PE's posts), while present-day C41 films apparently do not require a stabilizer for the stability of the dyes. Hence, the stabilizer is often replaced today with a final rinse that does not contain formalin or a formalin precursor, although the presence of a precursor is still possible.
So in short,
@WilliamP, if your lab actually applies the stabilizer that your film requires for optimal permanence is a bit of a gamble. I don't know which flavor of the Fuji chemistry they use and even then I'd still have to root around in their MSDS' to figure out if it's an actual stabilizer or merely a final rinse.
If you want to be certain, you could indeed apply a stabilization step at home. The most straightforward method would be to dip the film in a weak formalin solution with a few drops of photoflo added (although I find the latter usually unnecessary for 4x5 sheet film) -
please familiarize yourself with any health implications and take proper precautions such as performing this step outdoors. This won't hurt the film even if it has already gone through proper stabilizer at the lab. Let the film dry; do not wash after running it through your stabilizer bath as this would simply wash out most of the formalin.
