These vintage imitation horn buttons came in a bundle of carded buttons. They look very much like horn; so how do you tell the difference between horn and corozo nut or plastic dyed to look like horn without a hot needle test?
Horn: Real horn feels cooler than plastic. The surface will show slight imperfections/variations, although this is harder to see if the button has been dyed a dark shade. Even if polished, it will tend to have a more matt finish than many plastics. Holding it up to the light should reveal a slight translucence. Process horn (ground horn mixed with adhesive then moulded) may show a ‘pick mark’ on the back where the button was prised from the mould. Horn is heavier than plastic, and smells like burning hair if tested with a hot needle.
Corozo: The buttons are dyed before the holes are drilled, so the paler, natural colour will show down the holes.
Plastic: The surface will be warm to the touch, even and smooth. A seam may be seen on the back or edge; use your fingernail to scratch over the surface and detect this even if you can’t see it.
My buttons have a smooth, warm, even surface. The walls of the needle hole are an even brown colour, not a paler corozo nut colour. The back is an even brown, unlike the mottled top. I couldn’t clearly see a seam, but my fingernail detected it around the edge. Definitely plastic, but would still look good sewn on a coat!