I’m looking at gem prices here on IGS, and I’m finding that price per carat is sometimes lower for larger stones of the same quality and color. Huh? In what market are larger gemstones cheaper? Not talking about melee where faceting labor is the biggest factor.
Which specific gem are you looking at? There are cases where small size stones are priced higher than larger sized stones of similar quality. Smaller stones might be more popular for jewelry use. Greater demand could drive up the price per carat of small stones. A stone that’s too large to wear as a ring stone won’t sell as easily.
i have noticed in certain gems the calibrated jewelry cuts in the VS, VSS 4/5 5/5 have a higher price per carat as well manly because of the ability to sell stones fast.
Prices per carat for larger stones are lower for cheaper faceted stones like the quartzes (citrine, ametrine, amethyst) and blue topaz. This is because beyond a certain size, very large stones become unwieldy and are less in demand for jewelry, which would be the main market for these cheaper stones. For more expensive stones, even if the very large ones are unwieldy to wear, they are still eye catching and 1) someone will wear even the largest stone and 2) the largest stones which are unlikely to be set in jewelry are still collector’s items. -royjohn
All of the above, but a couple of cutting factors to add as well.
If it takes 2 man-hours for a 3mm stone and 3 man-hours for a 6mm stone, the labor costs on a per carat are greater for smaller stones. The mass is not proportional to size, it’s often squared/cubed depending on cut, but cutting/polish time is based on facet area, which means that it’s less expensive labor wise to cut larger stones. Especially true for less expensive materials, quartz as mentioned above and synthetics. That said, this isn’t always true. Smaller cuts can get away with simpler designs, and hence less cutting labor, but with larger stones and some materials, more complex designs are generally needed. A point cut is simple and easy at 2mm, done in sapphire might have only one or two tiers on each crown and pavilion, and looks nice for melee. The same point cut at 6mm looks unfinished, or done in quartz might look cheap.
Some materials are harder to keep a desired color, and small stones that retain good color are harder to find.
Beryls (aquamarine in particular) and Kunzite are this way, as smaller stones go white even if orientation is correct. If you have a nice piece of material that cuts small stones yet retains the color, the rarity is greater than a larger stone that keeps the color. The color saturation in some materials is not high, but enough material will allow the color to remain when cut large. That adds cost to the rough generally, aqua that goes white when cut small can be had for under $1/gram. Rough that retains color in small sizes goes higher. Admittedly, there are some cutting tricks to try and solve this (deeper angles on the pavilion, higher crowns to move the light toward extinction) but it doesn’t always work.
Thanks everyone for the excellent explanations, and while i agree with what you all said, it doesnt explain to me why for example Oregon Sunstone Mystique color lists 2.5-5ct as being worth more than double the price of 5-7ct sizes.
Dispersion is a funny thing. It represents the splitting of white light into the spectrum of colors we see in the rainbow. A diamond sparkles more than a topaz simply because of higher dispersion (assisted by diamond’s higher refractive index). Most gemstones have an optimal “sparkle” size for standard cuts. If you cut a large stone you ideally need a greater number of facets to give it that oomph. Also, there is that volume factor. You need more metal and larger surrounding stones if the ring etc is to have the wow factor. Great if you want a knuckle-duster to snag on fabric etc.