Rainbow Salt Tray

I saw this idea for a rainbow salt tray awhile ago and was so excited to make one!  Here is the link where I got the idea http://www.learning4kids.net/2012/06/05/rainbow-salt-tray/
I finally found a good box to use for our salt tray.  I followed the steps for how to make the rainbow salt box from the link.  However, instead of just taping the paper together I covered the paper with clear contact paper, that way there is no way the salt will go under the paper.  It's a fun sensory play experience now and great for writing practice later!