It is possible to leave some areas without reticulation on a sheet.
The manner in which the artist ‘draws’ the torch across the metal
surface can accomplish this, the pattern the flame is pulling up out
of the metal can be led across the surface, leaving spaces and/or
creating higher, stronger textures in chosen areas. It is a very fun
technique to perform. Kum Boo is something I add to most of my
reticulated pieces, you do it on the finished item. There is a
reticulated neckpiece and bracelet on my artist bio