Using Mod Podge
I have had many customers use this item to seal their work and create a nice thin, but hard layer. It is available in craft stores and more for about $8 - $15 or so. Best of all, Mod Podge is water-based and non-toxic. Note that this item is non-toxic but not FDA approved as food safe.
After you have completed your project, it is now time to apply Mod Podge.
Apply a first layer of Mod Podge to your work and let dry 15-20 minutes.
After your first encompassing layer has been allowed to dry, go ahead and apply a second coat to the piece and allow to dry for 24 hours. Project complete!