Gold, alloys and strength / durability. Discuss!

[chrono]

I love high karat gold through and through but do not fully understand all the mechanics and properties behind it, hence this thread. I understand the basics of 10k, 14k, 18k, 22k and 24k and their various alloys, pros and cons, but there are a few puzzling things that continue to make me scratch my head. I've seen lots of Middle Eastern, Indian and Chinese extremely high karat gold with beautiful detailed designs. Many are worn regularly and appear to hold up very well.

1. How are they made? Cast? Hand made?
2. Why are some incredibly reflective and/or shiny? How is that done when there is so much detailing in the piece?
3. I always read about how soft high karat gold is, yet jewellery made in those countries hold up remarkably well, or at least better than I expected. Is it the alloy used, the process, a combination of the two or something else?
4. PSers always recommend platinum or lower karatage gold (10k to 18k) for a stone setting, yet I've seen very high karat gold stone settings. I have inherited many 22kt gold rings holding diamonds and sapphires which were worn on a daily basis. The design / pattern is still clearly visible and the original stone is very secure. Are the prongs somehow different? They don't look chunky to me. Or is it because they use more prongs? Mine have anywhere from 6 to 8 prongs but they are extremely delicate.

 

[Euphony]

A lot of the strength of metal does indeed come from how it is worked. I suspect a lot of pieces in higher karat gold are work hardened through fabrication or through tempering. The thing about modern jewellery making techniques is that there is minimal working of the metal between it being cast, and it being worn. More traditional methods of jewellery making often involved more forming in metal, which helps its overall durability.

To give you a prime example, I looked up the stats on sterling silver (the Sterlium Plus alloy sold by Stuller, to be specific.) When you cast it it has a Vickers Hardness rating of 65-70. Dead soft (fully annealed) it will be 60. You can actually work harden or temper that same metal up to a hardness rating of 110-120. That is a huge jump in its durability. Link to technical data: http://www.stuller.com/apps/images/kbpdfs/Sterlium_PlusTechnical_Sheet.pdf

For comparisson, this is a chart of various gold alloys: http://www.stuller.com/pages/51284/

24k gold is 30 and 22k is 74. I believe that those stats would be for the hardness directly after casting, which puts 22k on par roughly with silver, and actually a bit harder. So it is not quite the delicate metal people think it is. Comparing it to silver (especially fine silver) at you will see it is not as soft as many believe, and just as silver can be worked up in durability, so can gold. That being said, 24k is actually softer than I would ever care to use for jewellery.

I think it is also important to know that gold coming out of Asian markets is not reliably tested and labelled. There are not the same rigorous standards for being able to claim a certain purity level, and it has been my experience that 22k usually tests lower (often closer to 20k). I am dubious that anything hitting the market as 24k actually is. It is likely closer to a true 22k.

 

[chrono]

Euphony,

I am delighted that you found this thread and responded. Thank you. Yes, it makes sense that tempering metal will increase its strength, the same way that steel and aluminum is treated prior to being made into a piece of equipment or part to be used. I guess that would also explain why my silver and gold bangles never deform when worn. They are so much harder than the bangles purchased in the US.

Is the Thai baht (23K gold) not well regulated to ensure that the purity level is adhered to? What about those in Hong Kong and Singapore?

 

[Euphony]

I will do a little research into Thai 23k. I am interested in their enforcement process for that country. 23k seems very soft indeed and would need a fair amount of work to get it to a usable harderness. I am curious!

Every country is a bit different. England is insanely restrictive where you cannot even stamp your own pieces, whereas India is extremely lax and rarely tests at the claimed karat purity. I wouldn't be overly suspicious of anything made for export purposes, but a lot of gold purchased within the Asian markets as very high karat is unreliable. I worked at a shop that took trade-ins, and Indian gold never tested to karat. But I would hasten to add that it is not an accusation of deceptiveness, as it is just the result of their recycling process combined with lack of continuous checking. In North America we refine our gold more frequently, so it usually tests correctly. We are also required to stamp our trademarks next to the karat stamp so that we are accountable to that claim. Even at 20-21k the gold looks much richer and more lustrous.

ETA: Thank you for letting me know about this thread, Chrono. I find this stuff fascinating, and it give me an excuse to look into it! Gold alloys are fascinating to me. Like the way 14k rose gold is quite soft and gummy but 18k rose gold is insanely hard and brittle. And did you know they have invented "purple gold"? It is pratically usable, but still! Science in action!

 

[chrono]

I am very curious too because I've seen incredibly fine work done in Thai 23k. How does trade-in factor in Asia? I don't think the accuracy of purity will matter much due the way business is conducted. When 22k or 24k jewellery is purchased, the price is whatever spot gold is plus 2 to 3% added for the labour (design and workmanship). When it is traded in for cash or upgrades, the shopkeeper looks at the stamp and presumes it to be true and accurate. The cash or trade-in amount will be the price of the spot gold by weight, so the only loss is the 3% for labour. When purchased low and sold high, the consumer can make a lot of money, which is why many consider gold as cash, but that's a totally different topic. So since the shopkeeper takes the stamp as valid, does it really matter if 24k is really 22k? Well, at least in Asia...

Do share more about 14k rose gold versus 18k rose gold or whatever else you like. I, too, find this fascinating. Purple gold was invented at least 6 years ago or more. I saw lots of purple gold jewellery in Singapore back in 2006. I hear so much about its brittleness yet it seems very popular there.

 

[AGBF]

I don't want this thread to die. I have been interested in it since Chrono first posed her questions, but was afraid to volunteer to go out and research them! (The only way I could think of to research them was to go to talk to the bench jeweler who makes a lot of jewelry for me in gold of any karat that I wish. He is employed by a local jeweler whom I use. It was he who made me a set of 24K bangle bracelets as well as many of my custom platinum and 18K yellow gold pieces in which I have diamonds set.) I really have little first hand knowledge of how gold is worked. I do have first hand knowledge of how it wears, however.

Love this thread!

Deb/AGBF

 

[AGBF]

ETA: Thank you for letting me know about this thread, Chrono. I find this stuff fascinating, and it give me an excuse to look into it! Gold alloys are fascinating to me. Like the way 14k rose gold is quite soft and gummy but 18k rose gold is insanely hard and brittle.

Euphony-

You are implying that all 18K rose gold alloys are the same. Is this true? Is Italian rose gold the same as rose/red/pink gold made in the United States? Any batch made in the United States? I ask because I happened to be in my safe deposit box a few days ago and saw some bracelets I bought in Italy many, many years ago. (All Italian gold is, of course, 18K.) I used to try to buy a piece of rose gold jewelry whenever I could afford it when I went to Genoa when I was younger. I didn't notice the gold jewelry being brittle. (On the other hand, I didn't make the jewelry; I only wore it!)

Deb

 

[chrono]

I do have first hand knowledge of how it wears, however.

By all means, do share your experience. I think there are various alloys within each gold "group". I often read of various shades of rose gold which makes me think that each shade has its own composition.

18K "Red" Gold (18K)
Gold 75%, Copper 25%

18K "Rose" Gold (18K)
Gold 75%, Copper 22.25%, Silver 2.75%

18K "Pink" Gold (18K)
Gold 75%, Copper 20%, Silver 5%

 

[Euphony]

I apologize for my absentee-ism, but it is hectic for me right now because it is the annual SNAG conference (Society of North American Goldsmiths), and it is being held in my city and I am up to my eyeballs in commitments. I haven't had time to research anything yet.

There are actually two different types of high carat reddish gold I work with, and that is the 18k red which is very brittle and the 19k portugese, which is a lovely buttery texture. The latter is significantly less red when held side by side, but much easier to work. Unfortunately, all true 18k red is brittle and pretty much identical. At that carat if you were to add any silver to make the alloy more pliable you would be loosing the colour. 18k white goal is somewhat brittle too because 18k gold wants to be yellow and trying to force it to be another colour usually makes it less fun to work with. It is why I love yellow gold so much. Yay yellow gold!

There is a lot of variance in yellow gold alloys and colouring. And there is a fair amount of difference in white gold alloys, most notably whether they use nickle or palladium to bleach the yellow out, but also the percentage of nickle makes a huge difference to the look of the gold. Ultra white nickle alloyed gold is almost the colour of platinum, and doesn't need rhodium unless there are solder seams.

ETA: Thanks, Chrono! It is nice to see the variations listed. To be honest, my casting houses don't offer that level of variety, but I am actually thinking that what they refer to as "portuguese red" is actually what you refer to as "pink". It has enough silver to make is very nice to work with. However, what we call "red" is horribly brittle at 18k, but very soft and gummy (and more red-toned) at 14k.

I want to put in a disclaimer that I only speak from the experience I have. The world of a bench jeweller is actually pretty limited sometimes as you will not use every alloy under the sun, you will use the ones the designer likes best and what sells best. I am partially on this forum for my own education, so I am not meaning to imbue my posts with a false sense of authority. I worked for a goldsmith who had been at it for over 30 years and was apprenticed by Italian masters, and he mis-pronounces corundum! We don't always get it right. But I have had the pleasure of working with a lot of different metals, and am happy to tell you what my experience is with them.

 

[chrono]

Have fun at the annual SNAG. Not to worry, we'll always be here and checking up on this thread from time to time.

Interesting you mention brittleness in 18K white and red gold because I often read about 18K WG being used for important 24/7 wear rings yet never heard it cautioned as brittle. If I can request a bit of your time and effort, do you mind posting a picture of 18k and 19k red gold that you work with? No rush at all but it would be great for us if we can see what you see.

I am just delighted to be able to discuss gold with someone actually in the trade working with such metals firsthand on a regular basis! I, too, am learning from you and everyone else on PS.

 

[Euphony]

Posting a picture of 18k red versus 19k portugese will be highly unlikely, as my current employer doesn't use 18 red. He dislikes the colour because it is not red enough for him. 14k is a much richer red, so he always talks people into it and if they want more of a blush then he likes the 19k. My former employer, by contrast, wouldn't use 14k anything because they were Italian and didn't believe in lower karat for any reason. They only used red gold when asked for it, never for their own designs. It really is not a fun alloy. For instance, if you heat it then quench it, it will fracture internally like bullet proof glass.

I can post a picture of 14k red, 19k "portugese" and 18k yellow. It will give you a good idea of where it falls on the colour spectrum at least.

As for the brittleness of white, it doesn't pose any durability issues unless there is porosity at a vulnerable spot. White golds tend to have more porosity because nickle doesn't play well with gold. They are reluctant alloys, if you will. As long as the casting is good, then what I mean by it being brittle is that you are limited to how much you can work the metal before it cracks. When you buy white gold wire or sheet it is much more yellow toned than a lot of the casting alloys because it has less nickle, and is made to be able to be drawn and rolled down, or otherwise formed. I wouldn't call that stuff brittle at all. But it is assumed with the ultra white casting alloys that you will just polish and set, but otherwise leave it untouched. At most you may hammer a texture into it. It is not designed for you to bend and twist, and it cracks if over-worked. It is more a complaint of workability rather than durability. I have never had yellow gold crack on me while bending it, but I have with white.

It is always a trade-off with metal. If it is soft it will be prone to bending and denting. If it is hard, it is more likely to snap or break off. A good white gold casting will take more wear than most anything, and people are not lying when they promote it as an exceedingly durable option, but for my money I think 18k yellow gold is the best mixture of strength, flexibility and overall casting quality. I look forward to yellow coming back in fashion.

 

[chrono]

Very informative post about nickel's role in a metal's workability. Thank you. Can I trouble you to add more metals into the same picture?
14k red, 19k red, 14k yellow, 18k yellow, 14k white, 14k white

 

[Euphony]

You are making me work, Chrono! The dirt on the platinum is polishing compound because I wanted the finish to be consistent on the gold but was in a rush. The texture is the reflection of white paper towel, not anything on the rings. I took 17 photos and they all look pretty crappy, but this was the best. I cropped it to a detail because it is less distracting.


Some first hand observations: There is a world of difference between 14k yellow and 18k yellow (more than is even apparent in this photo). I originally had their orders reversed and immediately felt wrong about it because of how much more washed out the 14k looked. 14k is a funny beast because it can be more pink then the 18k, especially if it has been heated and there is firescale on it. 14k yellow is prone to that and can even resemble rose gold when someone doesn't take care to prevent the discolouration. However, freshly polished it just looks drab next to its higher karat brother. I can always tell the difference between karats in yellow even though I have friends that disagree.

Another observation is that the difference between 14k white, 18k white and platinum is negligible when polished, but the platinum will look completely different in a month. The two different karats of nickle white are similar enough that I wouldn't worry about mixing and matching, even though once it gets a bit of wear I can often spot the difference. With white gold the karat matters less and I wouldn't fret about karat, though the palladium alloy sticks out are much darker.

 

[chrono]

I've been told by other PSers that I am a hard taskmaster. No pain, no gain! Your added explanation is very useful to help make sense of what I see on my monitor. When you wrote that the difference between polished 14k white, 18k white and platinum is negligible, do you mean prior to be rhodium coated? I would imagine an unplated 14k white will show a yellowish tint.

 

[Euphony]

What you are seeing are the unplated alloys used in the shop where I work. They are actually very white and not markedly different from platinum when polished. There has been a lot of advancement in that area recently and the metal colour has gotten very white. But you are quite correct that mass produced jewellery would show a very large difference between white gold and platinum when unplated so I shouldn't speak so soon. There is more difference in colour between low-grade white gold alloys and ultra whites than there is between ultra whites and platinum in my opinion. My experience is only in custom jewellery where the metals tend to be higher quality.

A chart of the various white metals relative whiteness:

http://www.stuller.com/apps/images/contentBlock/X1/Stuller_White_Gold_Alloys.jpg

 

[mickeyvaibhav]

Re: Hot forging 18K gold alloy

Hello!
I am working on the forging of 18k yellow gold alloy(with 12.5%Ag and 12.5%Cu). Melting point of the alloy is around 890C. I wish to know the best forging temperature. Actually before forging the alloy undergoes for several rolling and annealing process. Please help me is someone has already worked on this or any suggestion would be appreciated.

 

[AGBF]

I just carefully read Euphony's postings on gold again and feel very frustrated that I cannot absorb everything she wrote. I hope that we keep this thread going; it has taught me a lot, even though I am too much of a novice to comprehend most of it yet. I am hoping to expand my knowledge.

Deb/AGBF

 

[LLJsmom]

Just from a user's personal experience:

I have worn specific pieces of 24 carat gold for lengths of time, day and night, for a stretch of 3-4 years. I know that it may get a little distorted. Bracelet links stretch a little but not excessively. Some very fine design work may dull or wear out, but usually not much. I became accustomed to the feeling of weightiness in my jewelry. I think that is why I like platinum. I want to feel it ON.

I love the boldness of modern, beautifully wrought 24 carat. Check out this website that is from a chain in Hong Kong that sells exclusively 24k gold in modern styles.

www.justgold.cc
I'm curious to see what people think about the pieces sold on this website.

Here are some of the pieces that I do feel comfortable wearing. None of these are justgold pieces. I will take some of those pics later. These are just the less traditional ones.

 

[LLJsmom]

With regard to purity of gold. If you go to any very traditional looking Chinese owned jewelry store (at least in San Francisco Chinatown), you will find almost ALL 24 carat gold. Even clasps are done in the same 24 carat gold, and you open and close them by just pulling the gold apart and pushing it back together. Pretty simple.

I have a choker made of gold leaves (I will try to post a pic later.) and one of my leaves got bent. I just un-bended it. My bracelets get longer after wearing a 2-3 years. It can "grow" a quarter of an inch. You will see and feel it. But I have never broken anything. I am sure that if I snagged it on a piece of hard metal and yanked hard, it would break. So I am just careful about not doing that. Bangles and solid pieces can get dented. But you have a market of millions of Asians in Hong Kong, China and Taiwan that prefer that and do buy exclusively 24 carat gold. (I am not familiar with the buying habits of other Asian countries.)

Just an observation...