yeah, sprays do the job nicely and fumes are easy to extract.
if applying eg. wood varnish by brush - its gonna smell....(long) but I know people use wood varnish with great result. it makes card more rigid (applied only at printed side), prevents paint sinking in quickly into paper/card and secures it after. but its usually more than one coat.
Be aware, there are different types of craft varnish - acrylic, enamel so on. I've used many types - cant really say which ones as I had whatever was available at the time (and rattlecans had changed graphics often to add to the confusion xD) . After application wait with second coat as if you dont, you will have white frosting appearing.
hope that helps
