Is it known whether the effects of a given chunk of red kryptonite are reproducible? That is, if the chunk made Superman tiny in one exposure, would this chunk always have the same effect or does it have a random effect?
As mentioned in the comments, in most versions of Superman, he becomes immune to a piece of Red Kryptonite after a day or two of whatever change it's brought on him. Other Kryptonians tend to suffer the same effects from that piece though (which has led to characters occasionally saving a piece that has affected Superman, or Supergirl, in one particular way, to use on the other, or potential enemy Kryptonians, should the need arise)
There are, however, freak exceptions, that could either affect him more than once or duplicate past effects or last beyond the "normal" 24-48 hour timeframe. Once, I recall Superboy was affected by a piece that had previously made him small making him large after it was exposed to some type of radiation.(Adventure Comics 315) I've always wondered what would happen if a piece of RK were broken up. Would each "sub-piece" have a different effect or what?