"So if the ink worked separately, that most likely means a refill would work as well. Let's try it with water now." He rinses out a teacup and uses it to fill the scratches. "Would you like to do the honors?"

"...This has all sorts of implications. We might be able to make scrolls with invisible runes, if we drew them with the kind of inks intended for temporary marking that vanish after awhile."

"And we can mass-produce items!"

"I meant the fact that water worked specifically rather than the fact that the grooves are reusable, but yes, we absolutely can."

"I'm not sure water implies invisible ink. But it's definitely worth a try."

"I would have said watermarks but I don't know if we could get those precise enough."

"Yeah... any way to get them thin might also leave gaps in the lines."

"But we can mass-produce magical objects. We're going to drive that man so far out of business he can't find his briefcase."

Cackle. "I want a Ring of Gyges. Well, probably a Necklace of Gyges, because, shapeshifting, but you know what I mean."

"Indeed. ...Perhaps we'd better not mass-produce that one for sale. I can think of far too many unethical uses therefore."

"That being the point of the original story, yes. Although can you imagine the price we could get for it...? Still."

"Well, yes, I suppose it is. Having a few on hand just in case doesn't seem like a bad idea...my sister could certainly be trusted with one, and almost certainly Daphne as well. The most mischief I expect those two to get up to with the power of invisibility is more discreet public displays of affection, and Daphne could certainly use it for the same purpose as yourself, namely greater freedom of movement." He pauses. "I wonder if it mightn't be possible to create some kind of invisibility that only worked while in fullform, so that other winged critters could enjoy similar."

"That sounds harder, and an invisibility object is already a job and a half compared to an invisibility one-time spell, which we don't know how to do yet - but long term, maybe, although an invisible griffin has many of the same questionable applications as an invisible shapeshifter or invisible human."

"It would at least be harder to do things like invade the privacy of attractive members of one's preferred gender in washrooms, which is what most of my peers seem likely to do given the chance to abuse invisibility, but quite. Perhaps some kind of service for casting one-time invisibility spells so they can at least go flying outside of an Avalon for a little while would be a good idea."

"Whether that's a viable service probably depends on how long they last, and it's obviously harder to do mail-order than objects would be, but yeah, that sounds like a good way to advertise and scrape up starter capital. You wouldn't believe the rents on storefronts inside the Avalon. Everybody's so crammed in and many critters don't have the option to just park somewhere else instead, so..."

"Once we've mastered that application of magic and have sufficient capital to purchase real estate, increasing the space available to such persons seems like a priority, if not necessarily an urgent one."

"Yeah. I don't have the first idea how this Avalon was enchanted. Maybe we can find a newer one somewhere with a living caster to ask. I'll try to find the one nearest where Charlie lives this summer."

"Yes, it does seem like the sort of thing best approached after we've more magical achievement to our names than boiling water with a spell copied out of a book."

"Just a bit."

"But better to have thought of it and written it down for later than not. It isn't as though we aren't going to have impressive magical achievements in the future."

"Unless we kill ourselves botching a spell. Anything we're not copying verbatim from the book probably needs to be double-checked, then again after a night of sleep to be extra sure."

"Granted. That...might actually be a valid reason no one's accomplished some of the things we're planning, if they're not confident of surviving excessive spell design."

"Yeah. We'll be careful. Safety first."