Homebrew PCBs

Is there a solution I can buy to change double sided boards into positive developement boards as I have a gross of double sided boards and heard of a way to apply a solution to them to use them in the other method. There is a pro way I saw on a web site does any one know of that way and is there a cheeper way than that pro chemical. That idea would save trying to sell the excess boards or going the Pulsar way and buying a expensive laminator.