Elmer's glue is a copolymer of polyvinyl acetate and polyvinyl alcohol. The borax provides a borate ion which reacts with up to three of the alcohol groups on the polymer thus creating a crosslink and gelating the solution. The problem with this is that the resulting gel will continue to crosslink and will eventually become hard and brittle.
We use this in preschool all the time. If you keep it in an air tight container it will last for months, maybe longer. I have some at home that my kids play with (it also has glitter in it) and it is 9months old.
Also, if you leave it on your keyboard too long it will flow under the keys and make a huge mess-so don't let it sit out for too long.
GUYS I ALREADY COMMENTED BUT YOU CANNOT MAKE THAT, but with that recipe you can make putty which is equally if not more cool. I think the picture is an actually cleaning thing.
Also, if you leave it on your keyboard too long it will flow under the keys and make a huge mess-so don't let it sit out for too long.