1. Cut a 1x10-inch test strip from the paper to be tested. Turn on the room lights, fully exposing the test strip for a minute. Avoid excessive exposure or daylight, as this will leave a permanent stain.
2. Dim the lights, and divide the test strip on the back into patches, drawing a line every inch. Mark the patches with fixing times from ‘45 s’ down to ‘5 s’ in 5s increments. Leave the last patch blank to use as a ‘handle’.
3. Place the whole strip into water for 3 minutes and then into a stop bath for 1 minute to simulate actual print processing conditions.
4. Immerse the strip into a fresh fixing bath, starting with the 45s patch, and continue to immerse an additional patch every 5 seconds, while agitating constantly.
5. Turn the lights on again, and thoroughly wash the test strip for 1 hour under running water to remove all traces of fixer, and tone in working-strength sulfide toner for 4 minutes. Then, wash again for 10 minutes and evaluate.
If the entire test strip is paper-white, all fixing times were too long. If all patches develop some density in form of a yellow or brown tone, all fixing times were too short. Adjust the fixing times if necessary and retest. A useful test strip has two or three indistinguishable paper-white patches towards the longer fixing times. The first of these patches indicates the minimum ‘clearing’ time. Double this time to include a safety factor, allowing for variations in agitation, fixer strength and temperature, and the result is the optimum fixing time. Be careful, however, not to use a fixing time of less than 1 minute, as it is difficult to ensure proper print agitation in less time, and patches of incomplete fixing might be the result. Use the optimum fixing time, but at least 1 minute for each bath, allowing the first bath to be used until archival exhaustion. After all, incomplete fixing is the most common cause for image deterioration.