Antique cast iron knob in bathroom starting to rust - what to do?
October 27, 2018 2:09 PM
I have an antique doorknob in the bathroom which is starting to rust due to humidity. I can easily manage the rust with steel wool once a month, but would prefer to not have to steel wool it monthly. Is there anything I can do to treat it? I'd prefer treatments that wouldn't change the appearance/feeling of the knob.
Linseed oil or tung oil would work too. It will dry (auto-polymerize) into a clear, protective varnish. No need to apply it thickly—just give the knob a nice rub-down, let it sit for a day or so, then the day after that oil it again. Should work nicely.
posted by Anticipation Of A New Lover's Arrival, The at 2:48 PM on October 27, 2018
posted by Anticipation Of A New Lover's Arrival, The at 2:48 PM on October 27, 2018
A ‘drying oil’ like boiled linseed or tung will need less frequent application and set up firmer, but imo would change the look and feel more than I’d want. It will look and feel like a glossy finish, not like cast iron.
I’d pick linseed over tung, but I’d do a nice thin coat of beeswax after steel wool first, and see if that doesn’t work ot the way I want for the next several (6-12?) months.
Also finally regular application of sebum should help. I.e. frequent use by humans and contact with human skin will oil it with human oil, and will protect against rust well. If you make it a point to rub it with your hands well for a few solid seconds once or twice a week, no further action may be necessary. So I’d actually probably start there, but I’m weird like that.
posted by SaltySalticid at 8:22 PM on October 27, 2018
I’d pick linseed over tung, but I’d do a nice thin coat of beeswax after steel wool first, and see if that doesn’t work ot the way I want for the next several (6-12?) months.
Also finally regular application of sebum should help. I.e. frequent use by humans and contact with human skin will oil it with human oil, and will protect against rust well. If you make it a point to rub it with your hands well for a few solid seconds once or twice a week, no further action may be necessary. So I’d actually probably start there, but I’m weird like that.
posted by SaltySalticid at 8:22 PM on October 27, 2018
Forgot to add my standard disclaimer that when you're done rubbing your knob (sorry, couldn't help myself) you should wet the rag and leave it outside somewhere away from flammable things until it's totally dry. Drying oils generate heat as they autopolymerize, and linseed oil in particular has a low flash point. That combination of factors can lead to a situation where you get a feedback loop of autopolymerization > heat > faster autopolymerization > more heat > fire.
You don't want an oily rag spontaneously combusting in your house while you're at work, so soak that thing in some water and spread it out on the driveway.
posted by Anticipation Of A New Lover's Arrival, The at 2:05 PM on October 28, 2018
You don't want an oily rag spontaneously combusting in your house while you're at work, so soak that thing in some water and spread it out on the driveway.
posted by Anticipation Of A New Lover's Arrival, The at 2:05 PM on October 28, 2018
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posted by Glomar response at 2:14 PM on October 27, 2018