Milk Invisible Ink
1\Dip a cotton swab into a shallow dish of milk.
2\Use the cotton swab to write a message onto a white piece of paper. Allow the milk to dry.
3\Dry the message for about 30 minutes.
4\Expose the message to heat. You can use a light bulb, candle/flame, or an iron. The milk will heat up at a slower rate than the paper, which will cause the message to reappear.
5\Now, your milk ink is ok, you can use milk invisible ink to make your poker cards.