hello martin
were talking small stuff here a couple of inches square tops but as there mechanical parts to be made ,need retain size or as close as possible.
while searching i keep coming across ceramic fibre sticks in sets of various grades that can be shaped to suit,seem bloody expensive for what they are but may be just what i should be looking at,

regarding texturing i cant find much info on it other than the usual sales patter,id like to do it myself, it seems ideal for hiding machining marks and looks great.
theres sandblasting which ive never done,but will shell out for if need be,but id like to try out filling the mold with an acid and leaving it for the required time.ta