In Pokémon FireRed and LeafGreen, the Black Glasses are found in the Rocket Hideout in Celadon City. More specifically, the Black Glasses are in the bottom-right hand corner of the third basement floor (B3F) and you must make your way through the arrow maze in order to obtain them.
There is no other way to acquire Black Glasses in the game (aside from trading).
The only prerequisite for getting the Black Glasses is that you must be able to make your way to Celadon City.
You reach Celadon City fairly early in the game by taking the Underground Path from Route 8 (west of Lavender Town) to Celadon.
Getting The Black Glasses
Step 1: Find The Rocket Game Corner
When you reach Celadon City, head to the Rocket Game Corner, which conspicuously hosts Team Rocket’s hideout.
The Rocket Game Corner is hard to miss – it’s the reddish-orange building in the center of town that looks like a casino.
Step 2: Enter The Rocket Hideout
If you head to the back of the Rocket Game Corner, you’ll see a Team Rocket member guarding a poster.
Talk to that Team Rocket member to challenge them to a battle.
After you defeat the Team Rocket member, you can press A on the poster, which will reveal a set of stairs on the right.
Once you walk down these stairs, you’ll officially be infiltrating the Team Rocket Hideout.
Step 3: Finding the Black Glasses
Once you’re in the Team Rocket Hideout, take the first two staircases heading down until you’re on the third basement floor (B3F).
From there, you want to walk through the little doorway/hole a few tiles left of the staircase.
When you walk through here, you’ll see a bunch of arrow pads on the floor. We have to take these arrow pads in a specific order to find the Black Glasses.
Step 1: Take the arrow on the left-hand side, which will land on the yellow pad just to the left.
Step 2: Take the arrow pad just under the yellow pad you’re standing on. This will spin you into another yellow pad tile.
Step 3: Walk left two tiles from the yellow pad we just landed on, then head south and take the circled arrow below (pointing right).
After you take the final arrowpad, you will land on a yellow pad. From here, you can actually see the Black Glasses on your screen in a Poké Ball in the bottom right hand corner of the floor.
Step 4: Just make your way south, out of the arrow pad maze room (if you hug the wall you can avoid a fight with the Team Rocket Member). Then walk east and grab the Poké Ball to receive your brand new pair of Black Glasses!
What Are the Black Glasses Used For?
The Black Glasses are a held item that increases the power of Dark type Pokémon moves. Black Glasses aren’t extremely useful in FireRed and LeafGreen because there are not a ton of Dark type moves available in the games (fun fact – Dark-type isn’t an original typing from the first Gen, so it’s not found as much in these remakes).
However, even equipping the Black Glasses to a Pokémon that knows Bite can give a huge boost to the damage dealt by that move.
So while you might have a hard time finding a solid use for Black Glasses’, they are still a pretty good item to have.