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.

And now she has a proper invisibility item, except for the durability and the not being jewelry. Have any of her earlier enchantments worn off or degraded at all?

Not so far!

Sweet. She puts the invisibility rock in her backpack when she next goes to Dungeons and Dragons. What bizzare challenges will Xavier throw at them next?

It's apparently the underwater section of the adventure; they are given temporary use of magic items that let them maneuver and are sent to an underwater dungeon to retrieve an object.

That's seriously cool whether it has anything to do with the cultists plot or not. Also she should totally make a breathing-underwater artifact, someday when she's learned a lot more and also gotten an online reputation for reliable artifacts going. 

This dungeon has some neat traps. The one that starts up a vortex in the water to trap people is especially tricky and interesting.

The people who want the object turn out to have been infiltrated by cultists! They wind up fighting to hang on to the object and can now haul it to its probable rightful owner.

Well hang on, what is this thing? Because a lot of people seem to be after it, and if it's a bomb or the key to release a sealed horror or something then maybe even its probable rightful owner needs to end up disappointed.

It's a sealed box with who knows what inside. They can't get the box open even when Joseph insists on spending fifteen minutes trying different things and taking 20.

On the one hand, that's ominous. On the other hand, that's metagaming. And maaaaybe it's just really pretty jewels in a really secure jewelry box. What sort of person is this probable rightful owner presenting themself as?

They aren't, they're far away; they've determined her identity by reading the cult's correspondence.

Well, if she isn't actively pursuing it, then she probably isn't planning to use it to unseal any horrors right this minute. Margaret's character votes to bring it to her.

The party agrees, by and large, and they set out, and the session ends.

And Margaret catches up with Brenda on the way out again. "Can I show you something?"

"- sure? What is it?"