Guys, damn. You're such useless cunts.
Be the change you want to see in the world.
Let's say this was you. How would you want people to respond if a joke you made just didn't land? Would you want everyone to be cunts about it? Or would you want to know how to make it better? We're adults after all, let's wrangle our emotions and help this guy improve himself, as we are improving our own behavior.
I say let's help him work shop it. I'll start.
Okay, let's diagnose this shit. Number one - little, tiny issue - use "practice" not "practise" because the biggest chunk of your audience is going to be American, and the most-understood language is American English. You're not exempted for being Australian or British.
Two, when I read the word "alchemy" I think of old-timey scientists like Da Vinci mixing old bottles of colorful liquids together, and I think of people trying to turn lead into gold. Not that's the picture I've got in my head: This woman using bottles of liquid, potentially to turn something into gold.
So you brought in none of those things. You gave us one thing to start, gave us something unrelated on top of that. The pieces of a joke like this have to come together in our head to get a reaction. That's vague, but let's just work through and maybe it'll become clear.
Let's see what's salvageable. Let's be generous and say it's an ironically bad penis-pun attempt, which we get a lot of on Reddit. Common, but reliable. So, let's raise one eyebrow and smile goofily but wryly to get in character, and think of some possibles:
Okay let's grab one off this list and do a quick one. Now, I'm not a professional, so it's going to be a shitty joke, but it's jsut to show how you do this.
Let's do french bread. It's french, it's a food, it already looks like a penis, so it's an easy one. Now she has to make that bread hard, what's a funny way for her to do that? You have to leave the loaf out for a day to make it stale. Let's keep the structure and give her an occupation - who leaves french bread out to get stale? Bakers and everyone else. So let's just do that real quick and see what we have:
Is she a careless baker? Because she's made my french bread into day-old french bread.
Yeah, not very funny, but do you see the structure? Let's do another.
The lightning one. The glass that's produced is called Fulgerite. What makes lighting? Cumulonimbus clouds, also know as storm clouds. She's the storm, your penis is the sand, she's going to turn it into fulgerite. Oh, and fulgerite is an unfunny word, so let's find an alternate - okay, there isn't a good one, but let's just do it.
Is she a cumulonimbus cloud hovering over a beach? Because she's made my pile of sand into lightning glass.
Not the sharpest imagery, but in context it's a clear double-entendre.
That's all I've got right now, but I hope I've helped a bit and I hope I've encouraged others to band together and prop each other up instead of just popping open another can of humanity's most abundant natural resource, unconstructive criticism.