Yes! Layered enchantment is a go, unless it ruins the endurance or something. This one also goes in her desk, and it and the other one both get labeled with what incantation and diagram combo they got, on what date. 

Rock number three is where things start getting weird. She gets it both cold and blue, in that order this time, then puts it on the invisibility diagram and tries to make it invisible (swapping "this rock" in for "me" in the previously tested incantation). She gets out the "I'm dead" letter for this one, and casts from the other side of the room.

Now the rock is invisible, but the light appears to emanate from its location.

That is, to break out the technical runecaster terminology, totally awesome. Is it still cold?

It is still cold!

What if she invisibles a rock and then englowifies it?

The glow spell fails, expending the diagram.

Weird. And she's starting to suspect that all the totally harmless failures she's had might be a dragon thing, in which case she should never try to teach this and probably shouldn't get a teacher of her own either. Fortunately that runecaster in the other Avalon she wrote to never wrote her back.

Fortunately, none of what she has planned requires stacked enchantments as scary as glowing plus invisibility. The invisible non-glowing rock goes in the garbage wrapped in several tissues; trying to hang onto an invisible rock sounds like a recipe for annoyance.

Next step: user input. She modifies her invisibility chant to say "While I am carrying this rock, make it invisible and hide it from all eyes." Casting while the (new) rock is on the table shouldn't have any visible effect, this time.

It doesn't work when she picks it up either, though.

This is really weird, and she rechecks her French a few times. Oh, maybe that's it: how about "Whenever I am carrying this rock" etc?

Still doesn't work. Uses up the diagrams, but doesn't work.

She really thought she had it there. She looks back through the dictionary of rune meanings for ones that look relevant to ongoing control during a spell, and goes over the enchanting book for any mentions of user input.

"Control" is a rune meaning, and the enchanting book mentions that obviously medallions can respond to user will and are locked to particular species and then individual users during their lifetimes, but whatever art let medallions do that is lost; the less lost state of the art is passwords or non-thought circumstance response.

Maybe "Whenever I am carrying it" is too much information processing to load into an incantation, then. "Whenever this rock is moving"?

That one works fine!

And that's enough for one day. She labels the motion-controlled rock, sticks it in her desk with the others, and goes to bed. Before she falls asleep she decides that passwords are probably the way to go anyway; then people can wear her enchanted jewelry as jewelry and have it to hand in case they need to be invisible or whatever in a hurry. 

The next night is game night again; this time Margaret doesn't bring the invisibility diagrams.

Brenda doesn't bring it up even after the session.

Next day, it's back to the magic science. She enchants a pebble with "Make this pebble emit light without heat whenever someone says 'glow'". "Glow" is also in French; she figures if her items' passwords aren't in her customers' native language it'll be easier to avoid activating them accidentally.

That one works. It is unclear how wide a range it has on detecting the word, but presumably not infinite, as Francophones the world over may have cause to talk about glowing things sometimes.

Yes, if it had started strobing that would have indicated an impressive yet annoying range. She tries various distances and volumes of speaking, including "out in the backyard in a conversational tone" and "across the room in a whisper", and if the back yard is far enough away she binary searches until she has a general sense of how sensitive the rock's "hearing" is.

Volume doesn't seem to matter at all, but distance does; it works at a range of about ten feet. It has made up its own mind on how long to stay lit when she speaks and has by some mechanism settled one on minute and twelve seconds.

Distance mattering and volume not mattering is super convenient, but she still doesn't want an invisibility pendant that can be deactivated by a random passerby stringing the wrong phonemes together. She spends several consecutive evenings assembling the French for "Make this pebble emit light without heat whenever someone touching it says 'glow', until such time as someone touching it says 'cease'." How does that do?

That also works! (The default light color seems to be pure white.)

She can't actually test if a person who didn't activate it can deactivate it, but it seems pretty likely that they can. Next on the agenda is getting a thing to affect something other than itself. Time for another multi-day round of incantation design! Then the puts the next rock on the invisibility diagram, and incants what translates to "Make this rock turn itself and its holder invisible, from when its holder says 'hide' to when its holder says 'reveal'." (French's lack of gender-neutral pronoun is annoying, but the magic doesn't seem to be grading her on how nice her sentences sound.)

This works but leaves clothes visible. A straightforward incantation adjustment fixes it.