Hole Gauge (11.04)
For rough weight estimates, a hole gauge can be used. This is a metal sheet with a progressive series of labeled cutouts (holes) to match the shape of the “unknown” stone. The holes are placed sequentially over the top of a stone to identify its size. When the stone slips easily through one of the holes, you know the stone’s weight estimate must be less than the corresponding labeled weight. When the stone is mounted, it will not slip through (due to the interfering prongs), but the outline of the hole can still be used to arrive at a rough estimation. Some hole gauges also have extended round tabs that match the holes; these can be used to check mounted size by laying the tab over the the visible diameter. The gauge weight labels, correspond to the normal round brilliant proportions for each size.
Another method -- one that is especially effective for melee -- uses a more complex variation of the hole gauge -- the sieve. It consists of a series of hole gauges (punched-out plates) that can be placed in a cylinder to separate the various sizes of stones. Sieves are only used for loose diamonds in smaller sizes.This method is very useful if you intend to deal in melee.