Can You Get A Small Crack Fixed on Old Art Pottery?

Yes, you can get it professionally fixed.

As far as collectible value goes though, while a repaired piece (and you can tell under a black light) is worth more than an unrepaired piece, it is worth considerably less than a mint one.

A professional repair is generally only worth doing if 1) you're doing it for sentimental reasons, not money (because it was your grandmother's, for example) or 2) it's a large, expensive piece worth $500 or more. That's true of some Roseville, but not most of it.

If this is a functional piece of pottery there are businesses that do restoration. However, if it is a piece you have for antique value, it is best not to do anything to it, otherwise it will lose value.

Yes, by a skilled artisan.

However, that skilled artisan may well tell you that your piece is actually more valuable with the crack in it rather than having a modern patch-job repair done on it.