Unremovable dust

I process B&W 4x5" sheet in trays, up to 7 with the shuffle method.

I have a few time noticed big dust spec. that seem to be sticked to the emulsion. Last time, I noticed such an inclusion on a still wet sheet, on the last wetting agent bath and I couldn't remove it by gently rubbing. It eventuelly got off with scrathing but so did the emulsion. The sheets were pre-soaked before developping and they came out fairly well exposed/developped.

 

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Thanks for any hint or suggestions.

Some of the particulate matter you are finding may come from the water you're using to mix your chemicals. If you're using ordinary tap water, try switching to bottled distilled or purified water. Many years ago, I lived in New Hampshire and had a devil of a time with embedded particles in the emulsion until I switched to distilled water. If the volume of your work will allow, a top notch filtration system may also help.