Tiny Spirit Slates

The performer shows two small wooden boards and asks to a spectator examine them. Meanwhile, another spectator selects a card from a deck. Without any strange movement, the deck is given to be shuffled by the assistant.
Now the magician places a small candleholder with a candle in the center of the table, and asks a spectator to light it with a match.
Then, he puts one slate over the other, ties them with a ribbon and puts a piece of chalk above. The slates are placed beside the candleholder.
The spectator mentions his card close to the candle flame, like a ritual, and then the magician unknots the ribbon and shows that now the name of the card is written in chalk on one of the slates.
Remember: The slates are examined by the spectator!!

You receive:
2 wooden tiny slates.
One plastic small candleholder
A candle
A piece of silk ribbon
A chalk
A matchbox 
Instructions
And gimmicks