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Yellow stain after fixing

There is useful information regarding fixer use in the Ilford Rapid Fixer document. It advocates 2-bath fixing on page 3 column 1.

Read the information on page 4 beginning with the bold heading Silver Concentration and the following paragraphs to the bottom of the page (2nd column). In particular, read the information beginning with

“Prepare the testing solution by dissolving 2g of sodium sulphide in 125ml of water.”

https://www.ilfordphoto.com/amfile/file/download/file/1833/product/711/


From a Google search:

“Key points about yellow stains from rapid fixer:

Under-fixing:

The primary reason for yellow stains is not fixing the print long enough in the fixer, leaving silver halide crystals that can oxidize and turn yellow over time.

Insufficient washing:

Even with proper fixing time, inadequate rinsing after fixing can still leave behind fixer residue causing yellowing.

Old fixer:

Using old or overly diluted fixer can also lead to poor fixing and yellow stains.”
 

Good to learn. Thank you.
 
Under-fixing:

The primary reason for yellow stains is not fixing the print long enough in the fixer, leaving silver halide crystals that can oxidize and turn yellow over time.

This "yellow stain from incomplete fixing" is a profoundly different effect from what Alain Deloc reported. Alain's stain can be wiped off with a paper towel.

Insufficient washing:

Even with proper fixing time, inadequate rinsing after fixing can still leave behind fixer residue causing yellowing.

Alain's film is washed more than long enough. The "fixer residue causing yellowing" would do this weeks after drying, not right away.

Old fixer:

Using old or overly diluted fixer can also lead to poor fixing and yellow stains.”

Alain's fixer was mixed from fresh concentrate.
 
FWIW, I read Sirius' reference to fixer as being "formally" known as hypo as either a typo or an error in diction.
The correct reference being instead: fixer was formerly known (colloquially) as hypo - from the relatively archaic sodium hypo sulfate.
Proof readers and pedants unite!!!