The Mirror of Erised began as sea glass but then one day a princess ( who also turns out to be a witch )
finds the sea glass. she was the happiest girl in the world and she thought "Well this piece of sea glass is really reflective! I think I'll use it use a mirror." So she got some other people to find the other pieces of sea glass and put them together. together they were the size of a very large mirror. She looked at the mirror and thought for a second
"Ah, thats what it's missing! it's missing a frame!" she said. her servants quickly framed her mirror and in 3 days hence it was the most beautiful mirror in the land. The princess lived a life of happiness until she died of old age.
Later the princess's daughter took the mirror and when she looked into the mirror she saw not her reflection but what she wished for. The mirror showed her a image of her being the fairest lady in the land with her mom standing next to her. Proud of her for being what she once was. She was driven by madness. She stayed by the mirror until the invaders attacked and brought down her kingdom and the castle collapsed. Later the invaders found the mirror and had wars over it until it fell into the hands of Albus dumbledore, Albus hid the mirror in Hogwarts... and the rest is history.