Well, Elspeth is eager and waiting. She’ll open the door. Does she recognize any of the minds? 

Outside is a canal boat carrying several large boxes, two teenage boys, and an older man. Elspeth doesn't recognize any of them. The man greets her.

"I've a delivery of alchemical supplies and breakfast. Can the archivist confirm receipt?"

He gestures at the boys and they heft the boxes to carry inside. One does distinctly smell of breakfast.

It has been far too long since Elspeth has had anything meaningfully red to drink… breakfast indeed… she gives herself a shake. 

“You will want Dainan. I am a guest here, and do not know how to call for her. My apologies.” 

The man steps forward and taps a chit of bronze against a bronze plate on the outside of the doorframe, then leans around the door and knocks on another plate on the inside. A few seconds later a bleary voice sounds through the room, echoing as though heard through a long pipe, and Elspeth notices some of the sharply-defined local magic.

"Augggh. ...Hello? Person, yes?"

"Lady Archivist! Delivery's here. You scheduled it last night, food and alchemy. They said to tell you there was no filtering sand, the boat will be back with it in a day or two."

"Okay! Thank. Recorded now, bye."

The man seems to consider that acceptable, and directs the boys to set down the supplies. He gestures at the boxes as they're set down, identifying each to Elspeth. As well as breakfast, they also include samples of several metals and ores, local plants, some lumber, several soil types, some pieces of cloth, dyes, a small ruby, some tree sap, a stack of papyrus, ink, a jar of beer, a jar of wine, a jar of vinegar, and a jar of goat's blood, two live pigeons, a sickle, and a flute. After dropping everything off, he and the boys leave on the boat. Dainan can be heard rustling around a little more, upstairs.

Well, if immortality gives her nothing else, at least she’s learned patience. She will sit, wait, and get her potions project ready. 

Dainan stumbles downstairs a few minutes later, sleepy but upright. She wanders past the pile of alchemy supplies and towards a barrel of water, which she starts ladling into a tall, rectangular ceramic pitcher.

"Oh, guest. Hello, good morning! Do you need anything urgently? I'm sorry, I...need a lot of sleep."

The pitcher, like many of the objects around Dainan's home, has some specks of magic stuck to it, embedded somewhere inside. She triggers one on the pitcher, and the water inside spikes in temperature, roaring to a near-instant boil. She gets out a mortar and pestle, and a bag of leaves, and starts preparing some sort of tea. It doesn't smell quite like the tea Elspeth might be familiar with, more floral than herbal.

“I require no sleep unless recovering from trauma, but also I’m ageless so patience is easier for me than it used to be. I am happy to wait until you are more awake, though… come to think of it, if you want I could make you a potion? I don’t know how replaceable the components are though? Do you have cocoa plants here? Ginseng? Olive trees?” 

"Olives grow near here, they aren't too expensive. Some traders have cocoa, but I doubt there's any in the city right now. I haven't heard of ginseng. How's the potion work? This tea is pretty strong, but I don't like to take it many days in a row."

“Magic, mostly, but there are natural properties of the ingredients which anchor and amplify the magical effects. If you haven’t heard of ginseng then you probably don’t have it… everything else seems to have been translating- or common tongue, more probably. Hmm. Turmeric would probably work instead? Though I don’t expect a potion of alertness would be the most useful of the potions I know so working out substitutes is probably not incredibly worthwhile… I think it was mostly used by the wealthy as a cure for hangovers, and by scouts and guards for wealthy armies?” 

"How well does the potion work with repeated use? Someone who drinks enough of this tea can go without sleep for a few days, but they begin making more mistakes by the second day, and they'll collapse after four or five. Something more consistent would improve productivity by a lot... But you're right, probably something else is more important. I think you've mentioned that you use iron often? How cheap is iron, in your city? A lot of efforts are bottlenecked on materials strength, and the mining is cheap enough that we could use it even for construction, but it's very hard to work."

“Iron was expensive, but only because we had used much of it- and other empires more ancient than ours. Mining was the bottleneck because we had to dig deep and there were many terrible things in the deep places. Iron can be worked easily with sufficient application of heat, and with proper control of the carbon content…” she casts about for her drawings from the night before… here! “This is a blast furnace. We used them in Nuln. It… very simplified, it is a vertical shaft furnace with a powerful forced air current at the bottom which allows the fire to burn more quickly. You deliberately allow the carbon content to become higher and produce pig iron, brittle but hard. Later we refine that iron to create steel and temper it so that it is both flexible and strong. I took the liberty of drawing up a materials list here, if you would like me to create a small proof of concept?” 

"Of course! A proof of concept would be useful, I always like a model. This looks like it needs some specific sorts of clay. I think we have the ingredients, but do you know what kind of heat you need for firing the furnace vessel? Can it be fired in the kilns we already have, or do we need to have a mage prepare it?"

She pauses a moment.

"How long has your world been mining iron for? How much are you using? There's a lot of iron, even if you used it for houses I think it would take a long time to use up..."

“At a minimum, my world has been using iron in industrial quantities for at least twenty thousand years, and probably much longer. The types of clay matter less than the structure does, as long as the materials are able to take the heat. For the ceramic bricks specified here, I think they were usually made at around a thousand degrees- assuming our measurement systems match up and they HAVE seemed to so far.” 

"That's a long time! I don't think we've used a twentieth of all the iron in a twentieth of your time, and I don't think we've used a two-hundredth of the iron, either... But maybe we've used a two-thousandth? And I could see how you could use a hundred times more iron than we do, that sounds right. And then..."

She trails off, and flicks at a bit of magic, swinging some of her spellcraft up in front of her face. She scrolls absently through the field of nodes.

"Brick kilns are a thousand degrees under normal conditions. So it's fine, a mage doesn't have to help. That's kind of surprising, I would have guessed you needed higher temperatures to make stronger bricks. This doesn't sound too hard, then..."

She takes a large gulp of her tea, then shivers and takes another.

"I'll be awake soon, so we can get started. How much space do you need? Should we build something new, or go to visit the craftsmen?"

“This design only requires a footprint of about twenty feet by twenty. It will be about the same in height, but will produce significant smoke from the chimney here, so ought to be built somewhere that won’t be an issue. Best to leave some room about it for laborers to move around it, but thirty by thirty with adequate ventilation ought to be sufficient.” 

"Can do. I'll update the map..."

She wanders into another room and retrieves a bronze token, then triggers it and sends a bolt of magic flying invisibly into the distance. A few seconds later another bolt returns, and she feeds more power into the bound spell, which conjures an image in the air. It looks like a view of the city from above, as though looking down from a great height. Dainan peers at it, then points at a location.

"This plot is along the standard line for wood deliveries. Not that we couldn't do direct wood deliveries, but I assume a furnace needs a lot of wood? Copper and ink are processed here already, so no one will mind the smoke. Look big enough, or do you think you want a larger plot for more than this test?"

“Ah… wood? I had assumed coal. No matter, charcoal kilns are easy enough. That can be done with…” Elspeth draws a few more sketches. A rough brick dome structure takes shape. “…another twenty feet of footprint, about the same in height. More bricks of course….” 

"Coal? Where are you getting enough coal for forges? That's a real question, if you know a way to find a lot of coal. Coal is expensive."

“I suppose you could dig for coal in older mountain ranges, but that is honestly a lot of hassle when you can just cook wood into the next best thing. This…” Elspeth holds up her hasty sketch… “is a charcoal kiln. It allows one to… cook… wood into charcoal which is a lot like coal-coal except made of wood instead of naturally occurring. It will function just as well and, I suspect, be almost as much of a revelation for your people as steel…” 

"How much charcoal do you get from a unit of wood? In what way is it useful for it to be like coal? Is it the heat? I know that coal produces more heat than wood, but we haven't experimented much with that, since it's pretty rare. We never use it at scale."

Extrapolating from the immediate doubling of the required area, she also points out another, larger, area on the map.

“Coal- and by extension charcoal- are much more energy dense, and much more efficient, meaning yes hotter which is very extremely important. But also, you need fewer tons for a given project, and you get fewer impurities in the metal which is even more important… Yes, that new spot looks great.”