Looks like a saucer or soy sauce dish could be used for this purpose. Those things don't have notches, but it doesn't matter; they will release the large bubble one way or another.
They're not heavy enough and won't sink to bottom as fast as other watchers do.
The trick is they don't lift up from the bottom of the container they're in, just tip up a little, release the bubble, but more importantly hit with relatively great speed to stir the liquid from the bottom.
Ceramics have a specific gravity of at least around 2.2 or so; they sink like rocks, since they literally are.
> they don't lift up from the bottom [...] just tip
I can easily see a saucer doing the same thing: accumulating enough steam for the buoyancy to tip it up to release a bubble.
I don't suspect your physical intutition here is so accurate that you can declare that it wouldn't work, without any empirical trials.
Milk watchers may be massive, but perhaps that may not be necessary to their function. It could just be marketing: differentiating them from other objects and justifying their purchase. Nobody would buy a milk watcher if it looked exactly like a saucer, of which they already have eight at home.
Not everything that has mass actually requires it for function, and it can even be counterproductive.
Bicycles don't have to weigh 50 pounds, but cheap ones do, and they look rugged for it to the layman eye.
> Ceramics have a specific gravity of at least around 2.2 or so...
I think I failed to make my point clear. All milk watchers have a specific crevice volume / weight ratio, making them very hard to tip even under extreme conditions. So, the lifting force accumulating under a watcher is tightly controlled with the hole and the capacity of the crevice.
> I don't suspect your physical intutition[sic] here is so accurate that you can declare that it wouldn't work, without any empirical trials.
The problem saucers is their volume/weight ratio plus their asymmetric construction. Since they're not heavy enough, they won't be able to hit the bottom with the force required, hence fail to stir the liquid adequately.
Moreover, a milk watcher is symmetric. Even in an extreme case you can completely flip one, it'll continue to function. The moment the saucer flips, it's game over. Watchers have features to reduce their likelihood to fail.
Lastly, the internals of glass and ceramic watchers are slanted to further prevent lift-off, but to enable tip and hit back.
These features makes a watcher a deterministic device. Almost unflippable, with a tuned tendency to tip slightly and with a tuned weight to hit with enough force to stir the liquid. They are unhinged yet hinged wave machines.
The saucer is the complete opposite. A dome with a tendency to launch, with a low weight to crevice volume ratio, and no built-in mechanisms to prevent and recover from flips. A saucer has a tendency to launch up, a watcher has a tendency to "flip".
They are not marketing gimmicks. If they were they wouldn't be used in our home for 40 years, and I won't be continuing the tradition.
> Not everything that has mass actually requires it for function, and it can even be counterproductive.
Please, everything doesn't have to be light to function properly. Paperweights, door stops, wrecking balls, pool balls, throwing discs and throwing stones come into my mind. They won't work without their weight.
