I have an older skillet that Was used for an ash tray for about 30-40 years and I can't get it to stop turning cleaning water light rusty color. Any ideas?
I'd suggest, firstly, scrub past the rust on the surface using iron wool. Secondly, soak the skillet in pure distilled white vinegar for 6-12 hours. Don't soak it any longer as it could erode cast iron. Once you are done, season the skillet immediately to avoid further rusting on the surface. Hope it helps!
Maybe heat it up first to drive out existing moisture
Do you have old seasoning to clean off
If so that is a separate process
I would take some steel wool and polish it down
You can search You Tube for steel wool rust
Remove surface rust with steel wool
It might be so deep you cannot get past it with steel wool
If you have to resort to sand paper it is probably a no go
From the answer from SaurabhCooks (+1) clean / scrub with vinegar
Vinegar is weak acid and is good at dissolving rust
Then season / cure
I just cleaned up a rusty cast-iron skillet and I would like to season it