All About Pocket Knives

Here is a Wenger pen knife, model ? "TAHARA" with handles that i think are imitation tortoise. Is celluloid the only material that looks like these and was used for knife handles ? Acrylic has been used but the colors are brighter. Are these handles definitely celluloid ? or is there anything else it could be ?
Second is a Victorinox pen knife with what looks much like real tortoise, which usually is quite dark. But this is a relatively recent knife so real tortoise is unlikely. Somehow it does not 'seem' like celluloid. Any thoughts as to what these handles are ?
kj

Roland: I usually use two methods to determine whether it is real tortoise or celluloid.
First I look at it under a loupe;preferably a lighted one to see if there is any "layering" similar to ivory. If I can see that it is real tortoise shell.
If not I use method #2 aka the,"smell test". Take a dry cotton cloth and rub it briskly on the surface and if it emits a sharp odor then it is either celluloid or some other form of plastic. You can also touch your tongue lightly to the surface after rubbing it and if you feel a slight burning sensation it is celluloid.
Some people insist on using a hot pin to determine what it is. I believe that is akin to spreading acid on a metal handled knife to see if it is gold. JMHO my friend.
Some people say if it is backed up with gold foil it is celluloid although I have heard of instances of people doing that with real tortoise as well.