Gemjug Bath House
This trick is very simple and easy to use. All you need to do is obtain the Gemjug dance, which is obtained in the level "Mermaid Falls" by buying it from the snake women in the jar.
Once you're back at Scuttle town square, go into the bathhouse and transform into the Jar. If you are in the water, you will have unlimited magic and therefore can shake out as many gems as you want.
For even quicker results, buy the attraction spells at the shop so the gems will come to you, making it easier as you wont need to get out of your transformation near as often.
Written by Tyler.