How to mask areas on trumpet valves

[mcaswell]

Try our product MASK-IT

http://www.caswellplating.com/kits/maskit.htm

[plater12]

Hi I am plating some trumpet valves with copper and electroless nick but the bipass holes in the valves i DONT want to be plated,does anyone know how i can mask these areas,i plugged them up with paper but the copper went through,is there anything i could coat them with to stop the plate in these areas,i thought of nail varnish them use remover after but i dont know,any better ideas.
Thanks much