I heard that it contaminates the chemicals too. Usually they reuse the chemicals quite a number of times, so maybe the only shops that are willing to do it only do Xpro on the last time they use the chemicals before dumping it?
Well, one of the labs I asked about cross-processing happens to be one of the better known ones (at Peninsula Plaza), and this is what they told me, about it being bad for the machine.
Anyway, cross-processing is supposed to deliver un-predictable results, no? But I guess the most valid reason is chemical contamination? Again, I am not sure because as you say, labs that serve pros are more willing to do it, so I guess they must know what they are doing, and should be even more concerned about their output quality.
yes, that's correct, cos those lab people know very well about their machine, knowing what can do and what can not do to the machine.
other neighborhood labs, their boss never give a green light to the lab staffs to do cross-processing, and the lab staffs also have limited knowledge about the processing machine and photography, so you are asking them to do something unfamiliar, they would rather say "no".
beside, the technician who service their machine, will not recommend them to do cross processing, else their backside will get screwed if anything happen.
most of the pro labs people know photography very well also, and by seeing the film, they know which photographer is bluff one (they told me some pro photographers know nuts about exposure, can shoot bracketing from f5.6 to f22), so the pro photographer know they can't blame the labs for screw up their film actually, unless their film get jam inside the machine.
on the other hand, many people who using the neighborhood labs, conveniently put all blames of bad photos to the labs for screwing the films, even the out of focus and bad compositions photos also become the labs faults. I seen this happens with my own eyes.
so those neighborhood labs would prefer do something which is safe, familiar.
Thanks for all your replies, especially to Catchlights. Has given me a better insight.
I guess my main concern was whether I was doing the right thing or not. Didn't know that xpro is quite taboo(?) amongst some labs. The lab I go to has been willingly doing cross-processing for me all this while. In fact, it is they who introduced me to it! I also don't want to be responsible for "sabo'ing" people's machine lah.