Recently I have been decoupaging and I am a long time Mod Podge user for most of my decoupaging projects. The projects I don’t really care if they show age after a while and aren’t going to live long before making their way to the trash, recycling bin, or storage room I usually just mix cheap Elmer’s glue and water together. The tutorial for this easy decoupaging fix can be found at http://doityourselfdivas.blogspot.com/2011/09/diy-mod-podge.html I do not suggest using this tutorial for a sealer because Elmer’s glue will yellow. modpodgerocksblog.com explains more on why this tutorial is not a sealer.
Purchase instead a varnish or acrylic sealer. A spray can or paint will cost about $2 to $5, and any craft store or hardware store carries it. There is also this tutorial, http://www.woodooz.com/2012/03/how-to-make-your-own-mod-podge.html. They use acrylic gloss medium but if you like the matte finish look instead that is fine.
From what I have noticed from my own decoupaging experience is Mod Podge does last the longest and is one less step from adding a sealer which is why I prefer purchasing it (usually with a coupon because I am still broke) There are different brands of all-in-one sealer and glue out there. They usually are only cheaper by a couple of cents so it’s fine trying them out and finding out what brand what you like the best.
Well happy Decoupaging.