Exchange rate between the old and present value is:
The prices current for brilliants of ordinary size at the end of the seventies is best seen from the following table, which was compiled by Vanderheym, on behalf of the syndicate of Parisian jewellers, for the Paris Exhibition of 1878. Two brilliants of weights from 1 to 12 carats and of four qualities were exhibited, and the prices in francs given in the table are for the pair of stones:
The prices given in the above table of course apply only to the time at which it was compiled. A striking feature of the table is the difference, which exists between the prices of stones of the same weight but of different qualities, especially in the case of stones of the first and second waters. The difference between the value of a 1-carat stone of the first water and one of the second water is much greater than between stones of the second and third waters, and in larger stones the difference is still greater. Thus a 1-carat stone of the first water is worth almost three times as much as a stone of equal weight of the second water, the values of stones of this size of the second and third quality being in the ratio of nine to eight. The explanation of the apparent anomaly lies in the fact that in the Cape deposits large diamonds of the first water are rare, while stones of large size but inferior quality are abundant.
A consideration of the table will also show to what a small extent the values of diamonds at the present day are in agreement with the so-called Tavernier's rule, according to which the value of a stone is proportional to the square of its weight. While the value of a 1-carat stone of the first quality would be, according to Tavernier's rule, 110 X 12 X 12 = 15,840 francs, its actual value in 1878, according to the table, was 7,500 francs, or not quite half. The application of the rule to smaller stones results in a calculated value which is still further removed from the actual value; thus the value of a 6-carat diamond of the first water calculated by this rule would be 110 X 6 X 6 = 3,960 francs, while it is actually worth but 1,850 francs. At the present time, this tendency is even more marked than it was in 1878; the value of stones up to 15 carats is approximately proportional to their weight, so that a 1-carat stone is worth about double, and a 3-carat stone about three times as much as a 1-carat diamond. This holds good, at any rate, for the three inferior qualities of stones, but in the case of diamonds of the first water the increase in value is not proportional to the increase of weight.
The price of a 1-carat stone of the first water calculated by Schrauf's rule, according to which the value of a 1-carat stone is multiplied by the product of half the weight of the stone into its weight plus 2, would be 110 X 6 X 14 = 9,240 francs, the tabulated value being 7,500 francs; the value thus calculated, although nearer the mark than in the former case, is still considerably too much. As in the case with Tavernier's rule, the values calculated by Schrauf's rule for smaller stones are still further from their actual value, the calculated worth of a 6-carat stone being 110 X 3 X 8 = 2,640 francs while it is actually worth but 1,850 francs. At the present time the market price of a fine 1-carat brilliant is £15; in exceptional cases, however, £20 to £25 may be given for such a stone.
The price of stones of exceptional size, that is of those weighing anything over 1-carats, is not governed by rule, and depends very much on what a rich person or State is disposed to give for them. Diamonds of exceptional size and of unusual colours are not common articles of commerce, and their price, while always, of course, very high, depends on the number of would-be purchasers, which can be found for them.
With regard to the prices current for smaller diamonds, it is impossible to say much more than has been already said, for, after all, the value of stones of ordinary size depends to a very large extent on their quality. The price of cut gems and of rough stones always differs very widely; the latter are not, as a rule, bought and sold singly but come into the markets in large parcels, those from the Cape being carefully sorted and arranged according to quality, while parcels from Brazil consist of unsorted stones of all qualities.
Rafal Swiecki, geological engineer email contact
This document is in the public domain.