well, there have been no hits on this since you posted it yesterday, so ..I'm going to take a stab at it.

truth be known, the researchers of today, leave me so unimpressed with their findings.
chocolate used to be bad for us..
now it's good...first example~

and everyday, it seems that I see a television reporter, telling about a new research that seems to either upset or completely destroy the findings of yesteryear..

lead and cadmium in plates?
if it's in the plates, then for sure nipping them for a mosaic isn't going to upset your balance for either living, eating or anything close to dangerous for you or grandkids.

I have 8 grands and they eat on the dishes, lick them, if I make something they especially like..sometimes they drop them on the floor (handy for me)
sometimes they offer to wash them...that means touching.

this is my opinion, as a mother, grandmother, fellow plate breaker, nipper, crusher and mosaicer..

set that thought or worry aside....far aside.
you've made it this many years and have never had any incident of anyone you know or even know of, who has been taken to the hospital (and I'm guessing this)...
who has had any need for medical help, treatment or cause for concern.

if you do worry about it, then you can always use paper plates at home for food and switch completely to stained glass for any mosaic project.
or other pieces of stuff to make a mosaic..
the classification of stained glass and mosaic, surely does not mean to suggest it's only made from either plates, dishes or even glass of any kind, exclusively.
there are pieces of wood, rocks, shells, buttons, jewelry, sewing notions, fabrics, metals, brass, copper, tin, aluminum, trinkets, seeds, nuts, ...and all other finds, in yards, stores, trunks, garages, attics, junk drawers and closest...

the medical percentages of absorption of chemicals we ingest, either by airborne or ingesting is something to do a search of through the computer and I for one, would save it for an evening of complete boredom...and I hope beyond hope that you won't even consider sidestepping your artist license for fear of what dust comes from dishes.

this is in NO way, meant to criticize your worry...it's only meant to be one gramma to another gramma...
to go ahead and enjoy the art, not shy away from it, feeling that you could in some way harm those around you.

if they've been in cupboards for years, what the heck...break them and celebrate!

I don't trust the dollar store though...
and for sure, don't buy toothpaste from there, for kids.

Becky ;(*_*);

I think the lead thing is blown waaaay out of proportion.
As far as nipping plates-unless you are creating murals the size of texas from them daily-in others words nipping a LOT,I dont think there is any danger really. There is probably more danger to your lungs from the dust. In other words, if you are creating a lot of ceramic dust in an enclosed area it doesnt matter what it is it could hurt you. And that dust is probably more of a danger than all the chemicals could ever be.