They aren't going to be able to do that. There are no "ashes".
That would work pretty well, I think, since what you get back from the crematorium is not "ashes", but the skeleton, ground up. It's basically rock (calcium carbonate, mostly) and it doesn't burn very well. You can put enough heat into it to reduce it to lime, but that gets expensive.
So, they burn away the flesh, then feed the skeleton into a big grinder. Pop open an urn sometime and you'll see very white particles, about the size of BBs, give or take. It's not uniform in size. Kind of like very coarse sand, which is why I say it would be good for ice.
It's shockingly white, really, except for a few blackened sides that were on the outside of the bone.
Calling it "ashes" instead of "ground up skeleton" sounds more romantic, I guess. Well, less obviously offensive, anyway. I suspect sales would drop if the general population knew what really gets done.
OF course, that oven and that grinder never get completely cleaned out between bodies, so you probably have some of old Lester Philips who hated grandma and died a couple of days before she did, mixed in with grandma, and a bit of grandma hung around and got in with that troublemaker teenager who was always driving too fast and finally got what was coming to him.
That's assuming you are dealing with an honest crematorium, and they aren't saving money & time by tossing in several skeletons at once and then just divvying up the skeleton grindings among the correct number of urns.