Digital BW, The Print

A while ago someone mentioned a solution to this that involved printing a step wedge and 
then using something to spot prints with the undried ink.  The good thing about this 
technique is that it will work for both users of dedicated B&W inks and those printing B&W 
with colour inks (and printers of colour can use the same technique by printing a swatch 
of the image area they need to spot).  My question is on what material is the step wedge 
(or swatch) printed so that the ink mix is available and with what is it lifted and then 
placed on the image?  (I just tried printing to glossy paper with the ink saturation turned 
up but that didn't work.)  Is there some sort of plastic that will not absorb the ink so that it 
can be lifted off before drying?

Thanks

Steve