January 28th, 1891 — Ollivander's, Hogsmeade
In hindsight, he would realize the erumpent horn had been a truly terrible idea.
It was hardly the first time he'd experimented with new ingredients in his workshop; he tried new things all the time. He still hadn't entirely given up on the idea that he might strike upon some fantastic new wand core idea that would truly distinguish his work from his brother's; the wands he made now were fine, but they were hardly illustrious and he thought he could do better. He'd cycled through half a dozen novel core ideas, some of which produced decent wands but most of which were rather lackluster. When one of the dealers he used for phoenix feathers asked if he wanted to see any of his less traditional wares, of course Gideon had said yes. And when one of those wares had been a horn salvaged from a deceased erumpent, he couldn't pass that up. Erumpents weren't exactly frolicking in Padmore Park. He might never have the opportunity to do something like this again.
He'd bought it last week, and spent days drawing up vague plans for what sort of wand he might transform it into. If he sliced it thinly enough, he thought he could get maybe ten wands out of it — at least half of which would be unsuccessful, he imagined. So he had to go about this in a very targeted fashion, if he had any hopes of walking away with something brilliant.
It would have been an even more brilliant idea to have the horn cleaned out properly before he'd started slicing into it — the inside was still coated with the erumpent's signature exploding fluid. Which, predictably, exploded the moment it was struck, taking half of his workshop with it.