"- Margaret that was so dangerous -"

"I did a lot of research first. And simpler spells. And I didn't make the diagram myself, I copied it out of a book that promised it was good and I checked it over myself too."

"But the incantations, any time you hiccup you could die. I couldn't possibly."

"Well, if you don't want to I don't want to pressure you or anything. But I'm thinking of selling enchanted objects--there are some people who do it in Avalons or over the internet--so if I do end up making invisibility cloaks, do you want a freebie?"

"If you'd already made one, then - then yeah, I'd take one, but I just couldn't imagine - if you were showing me around outside and you tripped or a car honked while you were reincanting -"

"That's totally reasonable. Items are a lot safer than casting a bunch of times, and you wouldn't have to worry about us getting separated or losing track of time or something either."

"That too. I'd still want someone showing me around at least the first time."

"I can see that. I'd be happy to show you around town and non-invisibly open doors and stuff, if I get an invisibility cloak working."

"That'd be nice. But please, please be careful - cast sitting down and make sure you have enough air and everything -"

"I will, I promise. I never incant anything without lots of practice, too. It's nice that you're worried, but I am looking out for myself."

"If you say so."

"I do say so. And that was really all I had to talk about, so, see you next week I guess."

"See you," Brenda says with a weak smile.

Brenda is a sweetheart--and she is totally getting an invisibility cloak.

Margaret refines her design a bunch before starting to actually diagram anything. Inaudibility is an interesting concept, but it shouldn't be baked in, because someone invisible might still want to talk. The cloak should work without having to completely surround the wearer; instead of being invisible itself it should detect when someone is putting it on and make that person and anything else they're holding invisible until it's removed. Given that, there's actually no need for it to be a cloak; it could be a ring or a necklace or something instead and suit more different body shapes that way. Medallions are necklaces for a reason and that reason still applies. For that matter, there might already be invisibility items on the market; she should look those over both to make sure she includes all the features they do and to see how she can improve on them. 

One person is offering an invisibility ring labeled "vintage" and costing nine hundred and sixty thousand dollars.

Good to know that invisibility rings are possible in principle, but wow, even apart from the magic that must be some ring. Does it list features like the ability to disappear things you pick up, or any other details on its behavior? If she was going to buy something for the price of a very nice house she would want maximal details on what she was getting. (For that matter, is it gold set with rubies, or traceable back to Charlemagne, or something? Because seriously, what.)

It says to inquire for details. It's gold and looks like a snake with emeralds for eyes.

Seems kind of rude to ask for details when she's not planning to buy it and is in fact planning to compete with the seller. She'll do the design on her own. She comes up with the following feature list:

* Pendant (avoids sizing issues)

* Handle picked-up objects

* Visible when not being worn (too easy to lose otherwise)

* Can be worn over any body part

* Shareable when worn by multiple people (useful emergency feature)

* Unbreakable

        > (separate enchantment) (test if enchantments stack with something cheap first)

       >(charge extra?)

Before she can start implementing any of this, though, she needs to get a handle on the principles of enchanting. She makes a diagram that starts with one rune, "light", and cancels out everything else, and waits two days and checks it over, and puts a pebble on it, and incants the French for "Make this object glow green; make it emit light without heat."

Now she has a glowing pebble.

Is it heating up at all? Is it the shade of green she was imagining, or a different one? If she picks it up and tosses it in the air a couple times, does that mess with it? How about if she taps it on the table?

It's maybe a little bit warm but it's not getting warmer and it's not something you'd think twice about if you picked it up out of a sunny place on the ground. It is a different shade of green. Tossing it does not affect it, nor does tapping.

The light probably also behaves normally in relation to mirrors, photographs, etc, but it's worth checking. Then it goes in a dark desk drawer while she makes a stamp of the light diagram and gets ready to test enchantment stacking. She spends most of the rest of the week making another one-starting-rune diagram, this one with "cold". Is her first rock still glowing when she checks on it every evening?

The light does behave normally with respect to those things.

The rock is still glowing!

Excellent. That is now Endurance Test Rock; she continues leaving it alone. A different rock gets made glowy, this one blue so she can't mix them up. Then it gets put on the cold diagram and read her French for "Make this rock be cool to the touch, yet not as cool as ice." 

(She does not want an absolute zero rock, no matter how awesome that would be. Honestly it may have been some combination of luck and "insane dragon runecasting" that she didn't burn her eyes out with the light spell, or end up with a light too dim to see. Note to self: redo the light spell incantation again.)

Now she has a cold blue rock.