I have a few old molds from an estate. Some are Lyman Ideal (red box), others Lee. Most have a coating of rust, some worst than others. What's the best method of cleaning them up?
Thanks

I would hose them down with a water displacing oil and scrub with something like terry cloth or an old fluffy towel and make sure nothing is pitted.
Wipe off as much oil as possible, leaving no visible heavy coating or a shot with a fast evaporating brake cleaner can be used to thin the oil. Wipe off as much residue as possible, especially in the cavities themselves. Also change out the cloth when scrubbing until you quit getting the orange residue.

The excess oil can be burned off on a hot plate with the blocks open so they smoke out. Getting as much oil out as you can with a towel/cloth before heating will cut down the time the mold smokes out.

When it pretty much quits smoking, try heating the mould to casting temp an see how the bullets come out. I heat the bottom of the mould by putting it in fully molten alloy up to the bottom edge of the handles. When the alloy falls off, its up to temp. Open the blocks at let it smoke off again. Always do the dunk AFTER you've heated the mold good an hot on a hot plate.
Only when the bullets cast without wrinkles, pockets or voids is the oil all gone, but it does re-season the iron going through this process.

Pits in cavities aren't often curable, if truly at all.

I should mention a handful of q-tips or something similar to scrub and remove rust and excess oil; particularly in the areas of nose edges, driving bands, etc..

You can also do the oil scrub and remove excess with hot, soapy water too; be sure again to wipe out the cavities good, then heat up to cook off the excess water.

I've done both, but usually do the oil scrub/hot pad/lead bath because it provides some seasoning to the iron. Soapy water leaves it nekkid and dry.

Thank you HawkI. That was very helpful.

I routinely inspect my molds for rust, and even though they're stored in a strictly climate controlled room now and then some surface rust pops up. Mainly because I never ever apply oil/grease as a preservative. I just use either 0000 oil-free steel wool or the gray ultrafine 3M pads to whisk it off, paying close attention to making sure the vent lines are clear too which I do with a fine point stylus. Now and then though old iron molds fall into my lap that sport heavy rust and as long as there's no pitting in the cavities I've usually resurrected them using techniques much as HawkI delineated. If the cavity is pitted, it goes in the junk drawer along with the rest that are saved for use as the basis for re-cutting to custom cavities, which never happens.

The best solution though is to not let it rust in the first place. Or better yet go with aluminum molds.

You can store iron moulds still warm in heated canning jars to prevent rust.