Probably rentable for a day for a couple hundred gp, though there are few enough such goggles that it'd be a matter of going and asking individual wizards who have them -- in Cheliax most wizards get Arcane Sight off Hell instead, so the goggles are even less common. 

Magic items that let you cast spells with a duration 'concentration' are generally not possible to make.

So long as he's asking things anyways:  Is using direct Prestidigitation for all of his wall-writing purposes, in fact the sort of thing that trains his magical abilities at all.  Keltham just started doing that at one point, but then every time he did it, he was in the middle of class and it was the wrong time to stop and ask questions of Carissa about that, and at other times, he wasn't remembering to ask.

It'll probably make him better at Prestidigitation; it might improve his Spellcraft slightly but Spellcraft is one of those things where past a certain point that varies for each individual, you mostly only improve through deliberate practice not through incidental exercise of the skill. Carissa at the Worldwound made magic items for eight hours a day, which uses lots of Spellcraft, but then to actually improve at it she'd spend another several doing exercises where she tried to build her scaffold with a missing rung or something.

Right then.

What sort of exercises should he be doing.  Has he in fact been practicing in anything like the right way at all.

Yes! He has been given and is doing all the right exercises for someone who is new at it!!

Ah.  Okay then.

"You'll get there. You're actually progressing very very notably fast. If you were at a wizarding academy you'd have them talking about how quickly that one learns and whether to move him up a year."

Notably fast for 18 intelligence and already knowing all relevant math and having Security wizards if not Carissa Sevar watching him with Arcane Sight while he practices?  Or just around as fast as that should be?

(Keltham is not unaware that he has Protagonist Syndrome, and is monitoring its progress vigilantly in case it suddenly turns acute.  Well, more acute.)

Probably just around as fast as would be expected from that. 

Not 'yay' per se, but, his expectations remain calibrated in that case and don't need updating.

...separate question, if renting goggles costs a couple of hundred gp for a day, does that mean their actual cost is over 72,000gp, because that's what you'd earn off them in 360 days per year even if natural interest rates were 100%/year, or does it mean there's some kind of huge extra cost associated with renting anything?  And in the second case, can you, like, rent them for a whole week for only 25% more money?

- a big share of the cost, renting to a person you don't know well, is a guarantee that if they're lost or broken or cursed or something the replacement cost will be paid. You can buy guarantees like that from the Church of Abadar. Rentals would be lots cheaper if they were to someone you trusted enough the guarantee wasn't needed. She imagines there's some relationship between the duration of the rental and the cost of the guarantee but doesn't know details actually. 

This sounds like a weirdly low-trust equilibrium for a planet with truthspells and priests of Asmodeus.  Keltham suspects there's possibly something here about inadequate scales and institutions, like, there's no central Magic-Item Rental Agency that can form long-term customer relationships with people who could then rent lots of separate items much more cheaply...

Dropping spellsilver costs by a factor of 10 is probably a more sensible thing to get started down its critical-path first.  And maybe there's not that much market to be unlocked, with lots of short-term non-recurring magic-item rentals.  But it also could be the sort of thing where there's a lot of economic potential-energy pent up.  For want of institutions that can establish durable trust, wizards not making magic items that could be rented much more often, to many more people, more cheaply, while still making a higher overall rate of return.

Well, he'll also focus on his Spellcraft, though.

(Would alter-Cheliax have a higher trust equilibrium? Taldor sure doesn't. Osirion? Someone check rental prices in Osirion.)

"- I would be pretty excited about magic item rentals, because I like making magic items. It would be an economic transformation that would suit me particularly. So if you have more ideas on them I'd be interested."

Well, the obvious startup idea if this were dath ilan...

...Would be to find everyone who has a magic item that they do not strongly need on a daily basis, nor need suddenly on demand, nor would be crippled by needing to replace; and have a single company, that is the organization all the lenders trust, to be loaned those magic items, and to compensate them fairly for damage or loss.  All the renters know that, when they need to rent a magic item for a period, they can contact that company and see what it's got.  Instead of having a lot of isolated lenders and renters who don't have durable business relationships with each other, everybody has a durable business relationship with that startup.

Depending on how the scale ends up working out, you can amortize Teleport costs between rentals, like, instead of needing to teleport an item from Corentyn to Ostenso, the item goes on the daily or weekly trip from Corentyn to Egorian along with all other items rented from Corentyn, and then from Egorian to Ostenso along with all other items rented in Ostenso.  When items get requested often enough, the startup buys a copy of that item itself, instead of continuing to try to Teleport it around.

Zooming back out, the general question is how many magic items that somebody else would pay to use, that have daily uses or continuous uses rather than limited charges, are lying around somewhere being not already used on a daily basis.  Because that's a waste of that item.  Also or alternatively, which items would have daily or weekly rents high enough to quickly pay back the cost of their creation, even if there's no unused copies lying around.

That's the economic potential-energy within the whole system - a way that resources could be rearranged to generate higher earnings - and the question is just how to make the system slide down that potential-energy gradient, like catalyzing a chemical reaction.

" - permission to try that, if I ever have enough free time?"

"I had it in mind as more of a Project project, but you could make a play for managing it, assuming you're not too busy from being my second on the entire Project, which, in fact, you will be."

"If somehow the whole thing doesn't play out and the contracts end, you can take the idea and try to run with it, sure.  But there's a whole lot more advice out of Civilization you ought to hear first, if you were actually going to do that."

"Okay, okay, I'll be patient. I just really like magic items."

"Got any ideas for making that stinking spectroscope work?  It'd be nice if we could check candidate skill at learning to manipulate electron orbitals with Prestidigitation, and have a more objective measure of how good they were and how fast they were improving, before final tier assignments.  I have a couple of wacky ideas for getting the spectroscope running, but I don't want to contaminate you with mine."

Alchemy is not actually the area that comes most naturally to her but she'll try to come up with some ideas.

Alternately, if they were doing a magic item spectroscope, then she has tons of ideas, though it'd be very expensive and not a scalable solution.

Prototype first!  Scale later!  But Keltham is under the impression that item crafting takes more than a couple of hours, and he is looking for a way to get it within hours.  If he fails at that, it'll be time to drag out the magic item spectroscope plans.

Fair enough! They can spend some hours trying at the non-magical version.

Oh, he didn't say anything about it being non-magical.  Just that it wouldn't be a magic item.

Carissa is deeply tempted to cheat here by demanding advice from Avaricia but she'll have to just try with her own more muddled understanding of alchemy.

...also he thinks the whole thing with Carissa being impressive and correcting his Spellcraft, is, in fact, working.

Oh, good. 

- then he'll be delighted to hear she has yet more objections to how he grabs Prestidigitation after he casts it.