Should data tables be made in pen or pencil?
In the real world, chemists have a lab journal to document what they did; Good Scientific Practice guidelines state that results should be written there immediately, readably, non-removably, directly and a few other adverbs. ‘Great’ scientific practice or patent-safe documentation would require a witness.

In universities, I have heard of a trend of more and more lab journals being replaced by computer files. In the labs I have worked in, this was not the case and the paper lab journal remained the way to go. Apparantly, if you want to document something in a patent-safe manner, a paper book is mandatory.

Since the entries into a lab journal must not be removable, the only option you have is ink; usually, ball-point pens (biros) are used.



However, the wording of your question (‘chemistry lab’ and ‘data table’) makes me think you could still be a student. In that case, the only advice you should take is that of your teacher/advisor/…