Unfortunately, we can't trade anything other than treasure cards.
If you want to take a risk, you could both log in very, very late at night and you sell your reagent at the Bazaar. Your friend refreshes the reagent sales page quickly and buys the reagent ASAP. There's a risk that someone else could buy the reagent before your friend could get it.
I would like to give some black perils to a friend. Can it be done and if so how?
No. You can't trade reagents with a friend. The only way you can give them is to sell them at the Bazaar and make sure your friend is there when you do. Many who are needing the same reagent will grab them as fast as they show up.
You can't directly give or trade reagents to another player like you can with treasure cards... However, you can use the Bazaar in Olde Town, Wizard City to sell your reagents to other players! You and your friend could meet up in the Bazaar in the same realm and sell your black pearls so they could buy them, but be aware that someone else might try and nab them before your friend can.
Sorry, but you can't trade reagents like you can treasure cards. There is another way that involves the Bazaar.
If your friend needs black pearls I would suggest farming Pink Dandelions, they can drop Black Pearls along with Blood Moss and Springs. This might be easier, but longer.
If your friend really needs them, you and your friend can take a trip to the Bazaar. While there, you can sell your black pearls, then your friend can go into reagents and potentially find them to buy. It's risky because your friend might not find them in time, other people need these reagents too, and if you sell them at the Bazaar, other players now have access to them. The other risk is not having enough money - for example, selling 1 diamond at the Bazaar gets you 180 gold, but buying that 1 diamond costs 1000. If there aren't a lot of Black Pearls already there you risk not being able to afford them.