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What is the Ilford Photo Archival Sequence?

The ILFORD PHOTO Archival Sequence is a method of processing fiber base papers for maximum longevity while reducing the amount of water and time used.

The method, which was fully tested more than a decade ago, requires the use of a non-hardening rapid fixer mixed at film strength.
After the paper has been developed and stopped, it is placed in such a fixer for 60 seconds with intermittent agitation.
Next the paper is placed in a running wash for five minutes, followed by an immersion in ILFORD PHOTO Wash Aid (1+4) for ten minutes with intermittent agitation.
The end of the sequence requires an additional five minute running wash.

Checking Paper For Adequate Fix
It is easy to test for residual silver salts in the paper and thus check whether the paper is adequately fixed. 
Make up a stock testing solution by dissolving 2g of sodium sulfide in 125ml of water. Dilute this stock solution 1+9 with water for use. Place a drop of the solution on a white area of a print that is known to be well fixed and washed. Blot any excess solution. The barely visible cream tint that remains is the reference color for a well fixed and washed print. 
Soak any prints that show a yellowing of the test spot in fresh water for five minutes, then repeat the recommended fixing and washing sequence using fresh fixer.
A full, tightly capped bottle of stock testing solution will keep in good condition for three months. Once diluted to make working strength solution,