I think any varnish will do, but I prefer the 'ard coat simply for the fact that I'm only applying it just to the transfer and not the entire model and most varnishes I find are sprays. What I do is use the lahmian media to smooth out the paint, let it dry and then apply the transfer. Once dried I do a coat of 'ard coat to seal it and then apply the lahmian media again to take away the gloss left by the varnish.