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Almost all of the knives I used when carving my recent plaster piece have now rusted. Something in the plaster greatly increased the oxidization rate of the tools, which are primarily steel. Some I thought were stainless, but apparently not. The better tools, that are really stainless, are fine.

Is there anything I can do to keep them from rusting? Is there a solvent or cleaner I can wash them in after use?

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The grit in your plaster pits the surface of your tools, especially if the plaster still contains moisture while you're carving it. And then when you clean your tools with water the water gets into the pits and if left to sit there it will eat way at the metal.

Try to get the water off your tools as fast as possible.

After cleaning your tools with water, dry throughly with a dry cloth and then blow dry the tools to get rid of all the moisture (moisture hidden below the surface residing in the pitted surface).

There are anti-rust sprays. But in your case coating the tools with a rust inhibitor would not be a good idea as the coating material could stain your plaster.

Clean and dry quickly is my recommendation.

If you store your tools in a container with a lid thrown into the container a bag of silica gel desiccant. The desiccant will help absorb any remaining moisture.

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  • Can I keep them from pitting?
    – user24
    Commented Jul 17, 2016 at 0:52
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    Plaster by its nature is gritty. Any time it makes contact with the tool it will scratch the surface. Moisture is your enemy. If you store your tools in a container thrown in a bag of silica gel desiccant. The desiccant will help absorb any remaining moisture.
    – John Vukelic
    Commented Jul 17, 2016 at 5:04
  • Oh, good idea. You should add that part about storing them with the silica gel to your answer!
    – user24
    Commented Jul 17, 2016 at 14:14
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Plaster is indeed particularly bad for rusting steel. It helps a lot if you give your tools a light coating of a hard paste wax (eg car polish) before use. This creates a water repelling surface layer which protects them in the short terms and also helps prevent wax from sticking.

It is also good to keep a bucket of water hand to rinse the plaster off them as you go, while it is still wet. apart from preventing rusting this also stops lumps of plaster building up which make the tools less effective.

Immediately after use clean them thoroughly with water and a sponge and then dry them. WD40 is good for this as it actively displaces water (WD stands for Water Dispersant).

You can also give them a final wipe with an oily cloth or wax paste to give them a bit of protection untill their next use.

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