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I'm working on developing a realistic economy for my setting, but one thing my research has failed at is finding numbers that I can use to create a gem system that can be used to price gems of various quality. I'm aiming for a fairly simple system, even if that deviates a bit from history (though I'm trying to ground it in historical prices).

My goal is to, for a given type of gem, have a formula like:

price = (base price) * (quality) * (size factor) * (cut)

So that means that this question has a few parts to it. In all cases, I'm looking for answers in circa 1300 Europe (late middle ages, before wide external trade soured the market). Gem prices were fairly consistent across Europe at that time according to my own previous research (which didn't provide numbers for this consistent price). I can also convert between European currencies of the time, which were far less volatile than modern currency, so answers in any European currency are fine.

  1. What is the relative price of gems compared to each other? I know that the rough order is something like sapphire/ruby > emerald/diamond > amethyst/garnet/citrine > pearls > lesser stones (eg jasper), but how much would, for example, a 1 carat, well-cut, average quality stone have priced at (for at least the first 3 sets)?

  2. How does the price change with size? For example, in general, if you double the size of the gem (eg 1 carat to 2 carats), does the price increase by a factor of 2? 3? 10?

  3. What would be a good rule of thumb for cuts and quality? I'm thinking something like x1/2 for a dull stone and x2 or x3 for a particularly lustrous or fiery stone. Similarly, I was thinking maybe x1/2 for a poorly cut stone or x1/4 for an uncut stone. Is this reasonable, or are my numbers way off?

I know this is a bit of a long question, but any help with even one portion of one part of it would be greatly appreciated!

EDIT:
To clarify, I'm not looking for answers to "Were gems a major part of the economy?". I'm looking for "If someone had a gem they wanted to sell, how much could they sell it for?"

I've encountered multiple sources (one presented here) that gemstones were widely owned among the upper classes, and during the late Medieval period (which is the subject of this question) it was even a large enough market for forgers to get involved.

There are some sources that also provide some limited price information. The information from these sources is very useful for determining that the price of a ruby could be in the neighborhood of 1 pound sterling (expensive, but not prohibitively so for upper class merchants and above), but without details of what size the stone was, it's hard to know if this is an upper or lower bound.

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    $\begingroup$ There were no gem "cuts" as such in the Middle Ages. All their gems were cabochons. Hence, there was no such thing as a "fiery" stone; this is why brightly colored stones, e.g. rubies and sapphires, were priced more than diamonds. $\endgroup$ – AlexP Aug 20 '18 at 6:15
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    $\begingroup$ "What would the price difference be between a polished (cabochon) stone and a raw stone?" That depends on the specific place. Most stones came from the East or from Africa. In Western Europe there were no raw stones to be had. Also, I feel that you are vastly overstimating the availability of gems in medieval Western Europe; that is, my hunch is that there was no gem market as such, with clearly defined price scales. In Constantinople, maybe. $\endgroup$ – AlexP Aug 20 '18 at 6:35
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    $\begingroup$ To put in perspective the price of that "gold ring with ruby", £1 was the pay for a day laborer for six months. (From the same excellent Medieval Price List of Kenneth Hodges.) It was an exorbitant price. By "no market" I meant that they wasn't anything like an organized trade; AFAIK, regular trade in gems, with more or less general availability and more or less uniform prices began when regular commerce with the East was resumed. During most of the Middle Ages, regular trade in Europe was reduced to what was avalaible in Europe; gems are not. $\endgroup$ – AlexP Aug 20 '18 at 11:12
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    $\begingroup$ Also, some further consideration is that to pay a laborer for six months today would be about $3000-3500 (7.25 minimum wage for 30-40 hours a week, 26 weeks). That's actually pretty comparable to modern diamond prices for a small stone. So being worth such a large fraction of a laborer's wages would hardly preclude there being a market (just as in the modern day). Additionally, I've read sources that stated that in the late Middle Ages there was a gem trade, and even (qualitatively) stated that prices were pretty even across Europe. $\endgroup$ – Drazex Aug 21 '18 at 3:28
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    $\begingroup$ "It depends", like taking a Rolex to a pawn broker, it might work 10,000 dollars, but if you're hungry and haven't eaten in days you'll take 50 bucks. I imagine the medieval gem market was like that only more so. $\endgroup$ – Binary Worrier Aug 21 '18 at 12:06
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Doing a bunch of research, I've started to hammer out a system of gem values. Any feedback (or resources closer to 1300) would be welcome.

The first really useful resource I found was the Rapaport Diamond Report. This gives modern values for gems, but provides a lot of insight into how gems are valued. Simplifying the categories a bit (especially through removing distinctions beyond Medieval technology), we can see some basic patterns. From this, I created some approximate gem quality levels:

  1. Flawless: x3 value (This has no inclusions (flaws) visible with a jeweler's loupe)
  2. Superior: x2 value (This has only small, difficult to find inclusions using a jeweler's loupe)
  3. Average: x1 value (Inclusions are easily spotted with a loupe, but not the naked eye)
  4. Flawed: x1/2 value (Inclusions are visible to the naked eye)

Added to this, from the same source, we have a color value. The Rapaport Diamond Report is obviously meant for diamonds, but given other gems have ideal colors, I generalized for the sake of simplicity:

  1. Colorless (Diamond) / Rich Color (Other): x1.5 value
  2. Faint Color (Diamond) / Average Color (Other): x1 value
  3. Yellow (Diamond) / Faint Color (Other): x1/2 value

I found some very useful sources on understanding diamond pricing for color and clarity, which tied into the values for Rapaport.

For size, my first instinct from the above source was to use a quadratic equation. A helpful source confirmed that, c. 1592, this was an estimate being used in the trade. Although the source notes that it is no longer completely true for diamonds, it's apparently still used for other stones. So effectively:

the size factor is the square of the carats of the gemstone.

The main thing left, then, is to figure out the base values of the gems. Although the above source provides some numbers from a 16th century Italian goldsmith, it calls these numbers into question, with the ruby provided being either exceptional, or possibly simply exaggerated. Further, with other sources indicating that sapphires were valued above diamonds, the rock-bottom sapphire prices seem unlikely (or possibly a temporary market crash).

Outside that, however, there was little in the way of sources to figure out a base price. I opted then to take a page out of the Medieval Price Guide, where a gold ruby ring is priced at 26 shillings. Taking out a chunk for workmanship and profit, I used 20 shillings as an estimate for a base price for a 1 carat ruby. Given the mystique surrounding rubies, and their place at the top of the pyramid, I doubt it should be valued any less than this (though if it were a small or flawed stone, I wouldn't be surprised if an average stone would be higher).

Although it's suggested that a diamond would be worth 1/8 of a ruby, this seemed too low for my uses, so I increased it to 1/4, perhaps indicating its increasing price in the 14th century. This would give a base diamond value of about 5 shillings for an average 1 carat stone.

Amethyst was a very valuable gem back then, said to be valued equally with diamonds. This source is somewhat suspect, however, due to placing amethyst above ruby in value, so let's go slightly lower, with a value of 4 shillings for a 1 carat stone.

Sapphire is widely disagreed on, everywhere from our Italian goldsmith rating it as 1/10 the value of diamond, to others placing it neck-and-neck with rubies. Here I went with the value from Antique Sage of "twice the price of amethyst" ("amethyst was half the price of sapphire" in the original). That would place sapphire at a price of 8 shillings for an average 1 carat stone.

The only thing left is emerald, which is generally rated close to the top, so let's estimate 75% the price of a ruby (a value I got for a modern ring). That would be about 15 shillings.

For completeness, let's estimate any semi-precious stone (garnet, topaz, etc.) as about half that of the lowest stone listed before: Amethyst. That would give us 2 shillings for 1 carat.

The only thing remaining is the difference between an uncut gem and a cut one. Based on the amount of volume you're likely to use from gemcutters, let's estimate that the value of an uncut stone is 20% of a cut stone. A particularly good cut (the old Roman engraved gems, or a modern gem cut) is probably worth twice that of the standard cabochon cut of the time, maybe more.

That's what my research has yielded, but I'd be very interested if anyone has any sources that could further refine the historic "base prices" of the gems.

Edit:

I decided to check these gem values against what real terms I could. So I visited a store online. I managed to find the same ring (pictured) with various stones as a useful comparison of prices. Every one was on sale (likely a marketing ploy), so I've listed both prices for each as a range. These are all for one carat stones in a silver ring, prices in USD.

  • Ruby and Sapphire: 1725-2600
  • Emerald: 1300-2000
  • Black Diamond: 799-1200
  • Peridot: 200-300
  • Garnet, Blue Topaz, and Amethyst: 149-225

Based on previous work on the larger economy of my world, I estimated that 1 shilling was about 120 USD (based on commodity values and labor costs). So let's plug in some values...

  • Ruby: 20 s - 2400 USD
  • Sapphire: 8 s - 960 USD
  • Emerald: 15 s - 1800 USD
  • Diamond: 5 s - 600 USD
  • Amethyst: 4 s - 480 USD
  • Semiprecious: 2 s - 240 USD

This is actually very close. It may be worth increasing the value of sapphire (and amethyst with it), but other than those two and diamond (which was far less valuable before cutting emerged), all the stones are close to their undiscounted price in a modern market.

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Disclaimer: IANAEH(like IANAL, but replace lawyer with economic historian)

I have another take on your problem: Without some kind of central authority you cannot ensure that your price formula holds sway across the entirety of a large area like a province or a country. Also, there are other factors that will affect your price like perceived value of gems in that society, and availability of raw materials. A town situated on a diamond mine would most likely sell them cheaper than the capital city of a country that has to import diamonds and relies on them to buffer the prestige of its ruling dynasty.

Thus to my amateur view, what you need is a jewelers' guild or cartel. The cartel will then enforce your price formula across a geographical area of your choice, while absorbing all the factors that would otherwise cause prices to fluctuate.

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    $\begingroup$ That's a really good point. A jewelers' guild would be really useful both to help ensure roughly standardized prices, and to provide a central group for appraisal or sales (either directly or as an intermediary). $\endgroup$ – Drazex Aug 21 '18 at 5:09
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I'll present to you a basic scale of what I think everything should be and why I put it there. Its all relative, since I have no idea about currency types during that time period and what is considered a lot.

Base Price: 10 : This doesn't matter too much to me personally. You might want to tune it so its out of range of your lower and middle class and only for your upper class but that is going to depend on many factors like availability, skilled craftsmen, demand (and a lot of other reasons tied into demand) and/or practical uses.

Quality Scale: Arc Tan Graph +0.5pi (so it can start near 0): Basically at the very lowest and highest qualities, there isn't too much of a price change. For me this is because its going to be hard for a person to tell the difference between something that is 95% and 97% perfect. There is a quick increase in the middle 30%-70% region because you can notice the change pretty easily. You could put a sharp increase from 98/99 to 100 because a perfect gem would be easier to differentiate from a imperfect one if you really wanted to as well.

Size: Exponential : The larger the gem, the more it grows in cost. If you had size 1,2,3,4 the scale would be 1, 10, 100, 1000. Larger gems are often much more rare and so for me this should be reflected by exponential growth based on size.

Cut: Fixed Price * Linear Increase based on size: Firstly a fixed price for different types of cuts. But you also scale it up as the gem grows larger.

Basically for you scaling types you have the following choises Fixed -> doesn't change no matter what Linear -> steady increase proportional to whatever factor you chose Exponential -> keeps increasing at a faster and faster rate Sin\ArcTan -> slow change at the top and bottom of your curve and a linear section in the middle Logarithmic -> Fast change at the start and then slows down as quality increases

You could also use a Step function where the price increases after the quality passes a certain threshold or a x*sin(x) graph where the price always increase, but different parts that increase faster and slower, which could be tied to different tiers and levels within a tier itself.

Finally, just because a stones value can be calculated and set, doesn't mean it will sell at that price. The art and design of jewelry can really push up its price as well as the name and fame of the designer. While you often see this in art, you can also partially apply it to gems, so even if you do get a good system out, its only going to work as a minimum price that gets sold and should always be sold for a much higher price.

P.s. I haven't provided you fixed numbers because at the end of the day, it needs to be a scaling system that you are happy with.

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  • $\begingroup$ There are some good ideas here, but fundamentally, I'm looking for fixed numbers. I of course won't feel bound to make it 100% historically accurate, but the whole point of the question is to get a historical basis, rather than just using an arbitrary formula. $\endgroup$ – Drazex Aug 20 '18 at 9:54
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Only if your choosing Earth as the backdrop for your story would you be locked into using a system similar to our own. As I'm using a different planet, purely made up - though I did choose a near earth type planet that fit my requirements - everything else is pure a fiction of my own imagination. If you have such a planet, you can establish any set currency that you wish. Rather than gold being a common element as it is on our planet, I chose the metal Niobium to be the common element on my planet. Also Platinum which is in short supply here is more common on my planet as silver is here. I've kept in mind of course that humans require certain trace elements to function, such as zinc, sodium, potassium, and Magnesium. That being said, on my world gold and silver are more valuable due to their rarity. Consider how abundant gold was at the beginning of the gold rush, people picked up pieces of gold from river beds. I imagine a similar thing when it comes to gemstones. the lake on my inhabited island is full of neatly polished gemstones, naturally tumbled and polished due to the action of the water's currents as well as other factors. As someone mentioned above, you have to take into account proximity. there are people living on an island within my lake who marginalize the stones in the bottom of the lake, however when someone comes from the city, they place far more value on the semi-precious stones that these 'lochlanders' take for granted. the same can be said of my Merfolk, since I'm using mythological creatures. To them, pearls and Coral are so common that they place little value on them, however when they trade with the Citylanders, they put far more value in them, therefore, what the Merfolk are able to trade in exchange is much larger than the number of pearls or coral that they trade for food, tools, and clothing. one has to take into account also that values of currency were much different even as lately as the 70's. a carton of eggs and a gallon of milk were much cheaper than they are today, but someone from the 20's might not have spent such an exorbitant sum. As a previous poster stated, they didn't have many faceted stones in the 1300's. However they did have perfectly round rock crystal beads that were as clear as glass. As to karats and values placed on diamonds, I believe that was more of a Victorian invention. Colored stone were much more highly prized, though too the really vibrant colors only came later when we learned that firing certain gems changes their luster. I e. Ruby specifically, but I'm sure it works with others as well. you might be better off sticking to generalizations. Ie. a stone the size of a pea might have a small denomination attributed to it where as the size of a grape would be another or that of a walnut a third. One must also take into consideration that not all currencies were counted by metallurgy or precious stones alone. The spice Nutmeg was considered a commodity to the point where people carried their own nuts in pouches and could use them to trade, barter, or even sell for something of equal value. You may simply be over thinking things as I have wont to do. Hope this helps. p.s. I forgot to mention if there's magic in your world values placed on gems would be based of of the amount of magic they generate, or possibly the purpose for which the stone is intended. Rather than containing magic, your gems could merely be a conduit. a diamond or sapphire saturated with cobalt is an electrical conduit. Said diamonds or sapphires must be grown of course, but the theory is the same. Instead of conducting electricity your gems could conduct magic. As in Dr. Strange, magical powers were put within items that would otherwise use too much of the caster's own energy. by imbuing items with magic, it took the strain off the human wielding said magical item.

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  • $\begingroup$ The world is Earth-like, albeit with uncommon magic. Carats (that's with a 'c', "karats" are a measure of gold purity) were a measure of weight used for centuries, as clearly stated in sources going back to Renaissance Italy and likely before, as weight was the primary determiner of value (along with type of stone and color/clarity). Gem cutting and polishing has been in practice since Roman times, albeit faceting was an invention of the late 1300's. Further, a Ruby the size of a pea would be enough to bankrupt many people. $\endgroup$ – Drazex Aug 23 '18 at 2:36
  • $\begingroup$ So frankly, (1) this doesn't answer the question, in any capacity. I didn't ask for other uses of gems; I asked for numbers based on Medieval Europe because that's the rarity I want, with the ability to tweak it later. (2) Please do your research. Several statements here are incorrect. (3) Just because you decided to make arbitrary changes without considering the reasons (which is fine) doesn't mean others are "overthinking" if they want a historical or scientific basis. For example, why is silver less common than platinum in our universe? Why are some gems much rarer than others? $\endgroup$ – Drazex Aug 23 '18 at 3:09
  • $\begingroup$ since your the 1 posting the question, isn't it in fact you who needs2 do their research. I meant no ill by my previous post. I'm sorry if my answers were 2 general 4 you, I can't always remember all the reference material i've come across over the numerous years I've been writing. facetinghistory.com/timeline.html also here en.wikipedia.org/wiki/Gemstone en.wikipedia.org/wiki/Gemology en.wikipedia.org/wiki/Mineralogy gemselect.com/other-info/price-per-carat.php geologyin.com/2015/10/… $\endgroup$ – Vani Joy Aug 23 '18 at 3:46
  • $\begingroup$ I did do my research. In fact, if you look, you'll notice that the top rated answer at the moment is my own after I found some new sources. I'm still looking for additional numbers if people have them. I know you didn't mean any ill by it, but you failed to answer the question, at all. You weren't to general, you just didn't answer the question. It's like if I asked "How big is a tuna?" and you answered "I use crabs in my story instead of lobsters, and you shouldn't restrict yourself to using tuna." That's not an answer, even a general one. $\endgroup$ – Drazex Aug 23 '18 at 3:56
  • $\begingroup$ Your very first source states that faceting was introduced in the late 1300's, not to mention even diamond cutting (which is much more difficult than corundum) also started in the late 1300's. Most of those sources are very general, while the last two discuss exactly what I am asking for, without giving any numbers (which is the question). $\endgroup$ – Drazex Aug 23 '18 at 4:03
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According to your source, a diamond was worth about 7 pounds, while a ruby would be worth like 14 shillings.

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    $\begingroup$ Not really. The source is quite unclear on every point I asked above. (1) Rubies were more valuable than diamonds, so a similar sized diamond should not be more than 7 times the price of the ruby. (2) It says "two gold rings with diamonds", note the plural. This could be one giant diamond each, or dozens of diamonds; there's no way to tell. (3) What about the workmanship? What sort of artistic design does that price pay for? If my own source were a clear answer, I wouldn't have asked the question. $\endgroup$ – Drazex Aug 20 '18 at 7:45

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