Since 40 carats is large for a diamond, you can watch auction houses to find an auction for such a diamond.
As an example, The Emperor Maximilian Diamond sold at Christies in 2010 for US$1,762,500. Its documentation included this:
"[Report] from January 2010 from the Gemological Institute of America stating that the diamond is I color, VS1 clarity, with very strong blue fluorescence... accompanied by a supplemental letter dated 23 February 2010 from the Gemological Institute of America attesting to the re-cutting of the Emperor Maximilian Diamond from 41.94 carats to its present weight of 39.55 carats ."
What you have to sell is worth whatever someone will pay you for it. In October 2012, there were diamonds of about this weight sold at the Christie's sale. You can read more about the sales, below. In particular a diamond weighing just over 50 carats sold for US$9,500,000. In a ring, the mounting would be an additional cost.
Back in the 1950s engagement rings ranged in price from a few hundred dollars and up depending on the style, diamond size, and metal type. Remember, this period was shortly after the war, and money was tight. A small diamond (.15 carat) solitaire white gold ring would cost around $100 at that time. A ring with a .25 carat stone done in platinum would cost roughly $300 to $400. Any ring that was a filigree setting or had accent stones would cost more, due to the workmanship and additional stones.
250k
You can purchase a diamond of this weight today on Blue Nile and pay between US$55,496 and US$510,961, depending on the colour, cut and clarity that you want. The setting and the work to install the diamond into the setting of your choice will be in addition to the price of the diamond.
There are many websites that sell estate diamond rings. The best website to purchase from would be Ross Simons. They have a wide range of estate diamond rings at an affordable price.
Every diamond is valued by its cut, clarity, colour and carat weight, which together with the price of the metal in the ring would total the cost of a ring -- regardless of the year.
$60
The cost depends on which gemstone you choose to set in the ring. A diamond of this size would cost you multiple millions of dollars; a semi-precious stone would cost you much less. The most economical choice would be glass or crystal.
A 2 carat diamond cushion cut ring would make a beautiful engagement ring. The price of such a ring would vary from jeweler to jeweler; however, one could expect to pay from around $450 upwards.
Cubic zirconia rings are much less expensive than diamond rings. A cubic zirconia ring may cost around $700 while a diamond ring can cost upwards of $40,000. Cubic zirconia is a much less valuable stone than diamond is and cubic zirconia rings are priced as such.
The value of a diamond depends on its cut, its clarity, its colour and its carat weight. A local jeweler can give you the answer you want.
The value of a diamond depends on its cut, its clarity, its colour and its carat weight. A local jeweler can give you the answer you want.
A one carat diamond ring that costs $4,125 in 2013, sold for approximately $400 in the 1950s.
The cost of the ring includes the engraving of two names and a phrase on the inside band.
Black diamonds are a rare form and can be found in the African Republic and parts of Brazil. The cost of a black diamond engagement ring can differ depending on cut, style, and other stone settings. Front Jewelers sells black diamond engagement rings starting at approximately $1500.
The diamonds on the ring may be more valuable than the ones on the necklace.
About $800