Your sentence is not correct, but the problem has to do with "appearance," not with "characterize" (the more common spelling; your spelling is an acceptable variant in British English).
It is appropriate to use the verb "to appear" to describe both visual and non-visual aspects of a person or an object. For example: "I just heard from Fred, and it appears we're all going to be late to dinner."
However, the noun "appearance," when used in this sense, almost always refers exclusively to visual appearance. A substance may be transparent in appearance. It may be smooth in appearance--meaning visually smooth, not smooth to the touch. It may even be stiff in appearance--but I get the feeling that is not what you meant to write here, and in any case it is ambiguous, which is always undesirable in a lab report or other scientific writing.
You could use another form of the verb appear; for instance, this would be proper:
The sample appeared to be transparent, smooth, and stiff.
The sample appeared transparent, smooth, and stiff.
You could also use "characterized" on its own, to describe the object itself, not its appearance.
The sample was characterized by transparency, stiffness, and smoothness.
Better yet would be to remove the ambiguity altogether by rephrasing. For example:
Upon examination, the sample was transparent in appearance and smooth and stiff to the touch.
This makes it clear both how you observed it (visually and by touch) and what you observed (transparency, stiffness, and smoothness). "Upon examination" is optional but if your concern is that your language will be seen as too simple or "non-technical" it plays that role while keeping the actual sentence simpler.