Everything always seemed so easy on paper. Theory always made sense. Practice is where everything fell apart.
On paper, the chemical formulae was relatively simple. A stable mixture on a small scale was easy enough to accomplish, but making that large enough to mold it into a shape that resembled a monster? Good fucking luck.
Alphys spent weeks writing on walls and yelling at her chemical mix to function how it was supposed to before she figured out how to keep it stable enough to mold into a shape. The next problem was how much time it took it to solidify into the desired shape. Most of the test vessels were horribly warped by the time they became solid and Alphys was close to giving up by the time Frisk suggested yet another ingenious idea.
Humans make things from clay and resin all the time. What those things were the monsters had no clue, but it was obviously some sort of moldable substance the humans used. According to them the same problem persisted in some of the more liquid or slow drying materials and humans cleverly came up with an idea: a negative mold.
Alphys leaped on the concept so fast Sans was left spinning in place. With Frisks help they made a different material, one that dried quickly and wouldn't interfere with the other substance. They made bricks, first smaller than the human but quickly large enough to fit the king. It took some doing but Frisk had an idea of how it worked and worked with Alphys for many sleepless night to carve out a familiar silhouette.
Sans almost cried when he saw the negative shape of his brother carved cleanly into the rubbery cast. Several slabs lay discarded to be melted down and reused but this was clearly the best they had managed. Frisks hands shook something awful, but Alphys could push past her normal trembling with enough determination.
The pair told him they agreed that Papyrus should be the first one they try this on. They'd run the tests and made sure the slabs didn't bother the materials in anyway and they were ready to cast the skeleton, but they wanted his permission.
"P-Papyrus would be the m-most helpful!" Alphys explained quickly when he didn't say anything "He would t-tell us right away if, if anything was wrong, n-not that I th-think anything would go wrong!" She reassures, flailing. Frisk saves their panicked friend with a soothing gesture and looks at Sans.
[We have one chance. Dust not be reused. PAPYRUS most open to change. He have you to help] They sign with a sad smile. [You know him best. If he put on brave face you can know. Someone else might lie if sick or feel bad].
Sans heaves a sigh and nods his consent. It didn't sit well in his soul, his brother being a test, but they were right. Papy would absolutely speak up, if only to Sans. Open honesty was crucial to early projects and getting the desired results, a predictable and willing person was the best to start with. Frisk pats his breastbone gently in a reassuring manner. Papyrus was hardy and brave, honestly the best person ever, who better to help the next revived soul?
Unfortunately, the body was only half the problem. The other was him.
Meditating takes as much effort as the first time, and the ache in his bones sure doesn't help his already shitty sleep. To their credit, Frisk sticks close by and does their best to encourage him.
When not helping Alphys or sleeping Frisk is practicing what they preach. The meditate everyday, sometimes for the day, without a break. Apparently they're practicing control over their magic, so that when he's better they won't be holding him back. Their determination is, as always, impeccable. It's honestly impressive the way they push forward. As soon as they woke up after carrying him all the way to Hotland, Frisk was back outside, collecting the dust of dead monsters in jars and labeling them. Sans... chose not to ask how they knew which monster the pile belonged to.
People moved slowly back out of the Capitol at the kings urgings. They were so nervous, looking over their shoulders. It would take time for them to settle back down. Luckily, no one recognized Frisk. Doubly lucky, they'd finished collecting everything before anyone could interfere. People were upset they couldn't find the dust of their friends and loved ones, but an announcement from Asgore calmed them. He didn't say what exactly was going on, only that the dust had been collected and saved by the Royal Scientists and would, hopefully, be revived in the coming year.
After everything that happened, no one really had anything else to hope for. So, they accepted it. Every single one of them, without fail, took this project as their new hope.
Isn't that something?