First i am gonna dissolve citric acid powder in hot water, until a tiny amount stops dissolving due to supersaturation or just add 90g citric acid per 100ml water.
I then filter it through a coffee filter and pour some of the solution into an empty petri dish, and put a few strings into it
Now that tiny crystals have formed on the strings, i will choose the biggest. I use the old solution, and then suspend the crystal into the solution.
I repeat the process until the crystal grows bigger.