Hi. I was using an Ilford 1 1/2 grade filter on a 5x7 enlargement of a 35mm frame today. f/8 at 5 sec. in my Omega B600 with 50mm lens. This was giving me a good tonal range. I just got these filters and noticed this one was dirty. I washed it in warm water with a mild (natural) hand soap and dried it as best I could. After I did this, the next enlargement overexposed. Are you not supposed to get these things wet or clean them? Did I also possibly ruin this one?
The Kodak ones are gelatin coated polyester. When I used Windex and a lens wipe to remove a fingerprint the colored gelatin dissolved and left behind a messy mostly clear plastic filter.
I haven't tried washing an Ilford filter to see what happens. If they are bulk colored plastic - like a Rosco filter - then they should be cleanable.
I was able to clean some old Ilford MG filters. Years old of unknown provenance. The #3 filter was severely degraded compared to the others and parts of it came off with messy dye consequences. The others responded very well to wiping with a damp cloth and came out unharmed, but I would not recommend it.
The Ilford 6x6 filters I have get dusty and I clean them with a short blast of canned air. Even then they are not dust and scratch free but are used above the lens. The older Polycontrast filters used below the lens were much more resistant to a damp cleaning once in a while.
I tried to clean a couple of my 'under lens' Ilford filters before selling a spare set a couple years back... I cam tell you, Ilford doesn't like water either!
The Ilford under lens sets I have are either gelatin filters or dyed plastic mounted in the plastic frame. It is easily popped open and a new filter cut to size from the 3 ½ x3 ½ 12 set filer packs mounted very carefully of course, and with cotton gloves, I keep a package of them to replace the more used numbers that do fade over time. as all dyes do .
Under the lens type uses a square 2 3/16" piece. If you buy a 6" set, you can cut out 4 pieces out of it. I had to do that when I messed up mine. Apparently, over and under types use exactly the same material.