More information is needed about Western conditions (antibody source, concentration, freshness, incubation conditions, type of ECL reagent). Also, image of previous blot that worked well.

I usually find any black speckling is due to an old blocking buffer. Like if you use old milk powder. Similarly, if it hasn't dissolved properly.

Bigger black marks are usually from debris or fingers/ grease touching the membrane. Or if it has dried out (edges in particular).

With the lighter grey blotching, do you have excessive substrate on the membrane while imaging? I always try to pour the substrate off before imaging.

If you are talking about non-specific binding you will have to look at your blocking steps. Milk is usually best. Some antibodies just suck but given you had success in the past I would look at your antibody batch and blocking reagents. You might have to give your antibodies a centrifuge. Similarly wet transfer can give cleaner results than if you are using an iblot or similar

Warmest,

Lewis Williams In the end you were correct. We were using a Licor buffer, and switching to milk which was made fresh everyday revolved the issue.

Aj Boyland Excellent news! Glad to have helped :)