In supermarkets, recently I have seen plastic knives sold for preparing salad. If the label is to be believed, metal knives can cause some foods to have a metallic flavor.

These plastic knives look very cheap and do not seem well made. Has anyone tried them?

I think the idea may be a good one but plastic is probably not the best material.

I have read that, in the 1920s and 1930s, many department stores sold kitchen knives with glass blades to be used with fruits and vegetables. The selling points were that they were easy to clean, very sanitary, could not rust, and did not cause food to take on any unnatural flavor. The bad part was that they were made of glass, with all the disadvantages this implies. Apparently they were so fragile that very few survive to the present day--once upon a time they were very common, but now almost no one knows they existed.

I wonder how you would sharpen a glass knife. (yes, I can already hear you saying "very carefully!" :p)

How would you sharpen a plastic knife? With sandpaper? Or would you just throw it away and buy another when it becomes dull?

I have a plastic serrated knife. It really does slow down the browning of the cut edges on lettuce. I dunno about fruit, I doubt it would be sharp enough for that.

A more effective way of sharpening a plastic knife would probably be to press it into a hot mold, melting and reshaping the edge.

we should go back to using blades made from sharpened stone. It's so simple, a caveman could do it.

ceramic blade knives, if you can afford them, are miraculous tools.
they're much sharper than any steel blade and they never lose their edge and thats important because they shatter if you try to sharpen them.