She nodded. "I do. It seemed strange to me at the time that anyone should try to melt a stone, but I didn't want to parade my total ignorance to Caius, so I let it pass. What about it?"
"Well, " I went on, "almost all metal comes originally from stone, but not all stone contains metal. The stones that do contain it are called ore-bearing stones, the ore being, if you like, the raw metal. "
"You mean raw, as in uncooked?"
I nodded. "Exactly. Iron ore is red. Have you ever seen hillsides in your travels that looked as though they were rust-stained?" She dipped her head in acknowledgement.
"Well, that's exactly what they were. The rock that produces that red-stained effect is iron ore. We take that stone and we crush it and wash it thoroughly, and then we dry it over heat. The washing gets rid of the ordinary soil and other soluble material. What's left we burn at great heat in a tall kiln, or oven furnace, for a long time. In the course of the burning, or smelting as we call it, the metal melts from the ore and drips down into a crucible in the bottom of the kiln. We finish up, when the kiln has cooled, with what is essentially a lump of pure iron mixed with slag, the residue from the furnace. Then we go to work with our hammers, and by simply beating this mass— which is like a big, dirty sponge — we hammer out as much of the slag as we possibly can. It just falls out. and we are left at the end of the process with a lump of iron. We call it wrought iron, because it has literally been wrought out of stone by the sweat of our bodies and the pounding of our hammers. You follow me so far?" She nodded again, wide-eyed and obviously interested.
"Good. Now, here's where it gets complicated. This wrought iron is solid iron, and good for all kinds of purposes. It's easy to shape and it's easy to work with. But it's too soft to hold an edge. A mediocre hammered bronze edge is much keener and longer lasting than a wrought-iron edge. Of course, iron is almost impossible to work with when it is cold. You have to heat it to a red-hot state to be able to shape it. " She nodded, acknowledging this well-known fact.
"Right, " I continued. "Next step. Somebody, somehow, long ago. nobody knows when, made a momentous discovery. Everyone who worked with iron had known for centuries that to keep an edge on an iron blade you had to hammer the edge and then allow it to cool slowly. If you cooled it too quickly, the edge wouldn't hold. But somebody, one day, must have decided to re-edge a blade, and by accident must have left the blade in a charcoal fire for longer than was necessary at the time. He might even have hammered the edge into the blade and then reheated it. When he realized what he had done, he may have thought he had wasted his work, and then plunged the blade into water to cool it quickly, so that he could start all over again. Nobody knows how the discovery occurred. It was an accident. But the fact remains that iron, reheated in a charcoal fire and then plunged into water to cool quickly, takes on an edge that is unbelievably hard, whereas the same iron, heated without the charcoal and then plunged into the same water, will not hold its edge. "
"That sounds impossible. "
"I know it does. But it's true. "
"Is there some kind of magic in the charcoal?"
"There must be. " I shook my head, as I had done so many times over the same puzzle. "It must be magic, of some kind. But I don't believe in magic. And I refuse to believe that, with all the things in the world that are supposed to be magic but are not, there is only one thing, charred wood, that is not supposed to be magic and is. No, Luceiia, it isn't magic. It's just something that we don't understand yet. "
She smiled at me, a marvel-laden smile of warmth and admiration, and I almost stretched in the joy of it like a cat.
"No wonder, Publius Varrus, that you spend all your time over a furnace! That is absolutely fascinating. It can't be the water that softens the edge, so it has to be the charcoal. "
"No, quite the opposite. It's the lack of charcoal that makes iron soft. "
"Yes, the lack of it... that's what I meant. So the charcoal holds the secret of the hard edge. And nobody knows why. That is fascinating. "
"Isn't it?" I hurried on, revelling in her approval. "Of course, you understand that nobody caught on to this quickly. The hardening was a hit-or-miss process for ages. But gradually, a method for making hardened iron came into general use, and as smiths learned how to increase the heat of their fires, the quality of the iron increased from black to the pale grey colour of our iron of today. "
"Wait a minute. What do you mean, they increased the heat of their fires? What can be hotter than fire?"
"Hotter fire. " I laughed at the expression on her face. "That's why we force air into our coals with bellows. The air blast increases the heat of the coals. No one knows how or why. And some fuels bum hotter than others. Some burn more slowly. That's why we use charcoal. It burns hotter and more slowly than ordinary wood. It can build up to fierce temperatures. My grandfather almost gave up on smelting the skystone, as I have said. He had tried a number of fuels, different kinds of charcoal, and increased the flow of air to his furnace to an extent that he'd never tried before, but none of it had worked. And then, finally, when the furnace cooled after what he'd sworn to himself would be his last attempt to smelt the stone, he noticed that, although he had achieved no melt, the surface of the stone did look different somehow, almost as though it had started to change. So he resolved to try one more time, and to find some way of really increasing the heat in his furnace. By this time he had spent seven months fooling around with the thing, but it was his hobby, and he considered the time well spent. "
Again I noted the rapt expression on her face. She was far from being bored, I felt, but then I thought that perhaps she was merely pretending interest. I allowed my voice to lapse into silence, giving her the chance to change the subject if she so wished.
"Well? Then what? I know he was successful, but how did he do it?" The eagerness in her voice was genuine. I smiled and continued.
"He mentions in his notes that an associate of his — a merchant of fuel and oils — had found a deposit of coal that he couldn't use. Apparently, this coal he had found was too brittle. It broke up into tiny little pieces and it wouldn't flame. My grandfather remembered this. The man had not said that it would not burn, you understand? Merely that it would not flame. My grandfather knew that charcoal wouldn't flame, either, and yet it burned hotter than the wood it was made from. He became curious. He asked his friend to sell him some of the coal. The fellow snorted in disgust and told Grandfather where he could find it for himself, and wished him luck.
"Grandfather Varrus collected some of the coal and mixed it with some of his highest-grade charcoal to see if it would burn hotter. It did. It burned hard and clean, and by the time he had experimented with the proportion of coal to charcoal, he had evolved a furnace fire hot enough to smelt the skystone. The rest you know. He had enough metal to make the sword for my father, and this dagger for me. "
"But he mixed the sword blade with ordinary iron?"
"No, " I said. "It wasn't ordinary. It was his best. But Theodosius's sword is nowhere near as brilliant as the skystone dagger. " Luceiia had a strange and thoughtful expression on her face. I waited to hear what she would say. When she did speak, however, she asked a question that surprised me.
"How long ago was this, Publius?"
"No idea. It must have been just after I was born. My father left for the last time shortly after that. Thirty-three years ago? Thirty-four?
Something like that. I suppose I could pinpoint it exactly from the old man's notes. "