There are a large number of metals and metal alloys used in fine and artisan jewlery. Here I discuss many of them, and their strengths and weaknesses.

• Platinum: Platinum is a lovely metal! It is very unlikely to cause an allergic response, and its grey color looks lovely with both diamonds and colored stones. Unfortunately, I do not have the facilities to work with it. Gold and silver- the metals I mostly use- contaminate it, and it requires far hotter temperatures to work than I can achieve. I can use the occasional piece of platinum as an accent on a largely gold piece- but I do not work in Pt itself.
  
  
• Gold: Well, that covers a lot of ground! There are a huge number of gold alloys available now, with all sorts of qualities. I'll discuss here the ones I'm most familiar with.
• 22k+: This is the real thing- high-karat gold. 22k is 91.7% gold (24k is pure gold). These golds have a rich, luxurious golden color... but tend to be soft, so they do not hold up well to heavy use. Often people try to create sturdier alloys that have some of the rich color of the high-karat ones, but make the jewelry sturdy enough to wear. 22-24k golds certainly have their place in a jeweler's work, but we do have to keep in mind their weaknesses.
• 18k: This is the most favored "artisan" gold, partly because the 25% of other metals make it sturdy enough to wear, and partly because they also give one a range of colors to work with. The colors range from a very pink or red one with lots of copper, to a "green" with a lot of silver. My personal favorite 18k yellow gold is an alloy from Hoover and Strong called "royal" yellow; it has a richer, buttery color than most yellow alloys.
• 14k: This alloy is generally preferred for rings that will be worn daily. Because it has almost 42% of other metals (which are often not specified), it's sturdier than higher-karat alloys, and holds up well to hard use. Wedding rings are commonly made from 14k. Again, many colors are possible, and my favorite 14k yellow alloy is H&S's "royal" yellow.
  
  
• White gold: I've pulled this out specifically, because so many people are interested in it. Basically: gold is yellow. "White" golds try to diminish this yellowness by mixing the gold with other things.
• Nickel white gold: The most common white gold is in the USA is mixed with a large amount of nickel. This makes a nicely white gold alloy... but has several undesireable qualities from my point of view. The first is that nickel is probably the metal to which people are most likely to develop allergies. I am very reluctant to make a piece of jewelry to which someone may become allergic! It is also very brittle, which makes it hard to use with stones, and in my opinion, it's less capable of holding up to hard wear. I do not use nickel white gold in my work.
• Palladium white gold: An alternative to nickel white is palladium white gold. Palladium is a metal in the platinum family, and can be mixed with gold to whiten its color. The result is a grayer white gold than the nickel white makes- but it's not as likely to cause allergies, and has excellent working qualities, particularly for setting stones. This is my favored white gold. There are other "white" metal options, however!
  
  
• Palladium: This is a platinum-family metal that's 95.2% palladium. At the moment it's about half the price of gold, so it can be an effective alternative. It looks very similar to palladium white gold, although if you put the 2 next to each other, the gold is a slightly warmer color. Its main drawback is that there is not a really good color match in solder. I have some experience working with palladium, but have not done extensive fabrication in this metal. I think it would make a great choice for a Mobius ring- however I would at this point be reluctant to take on more extensive fabrication in this metal. It is slightly softer than 14k palladium white gold, and if you put it right next to the gold alloy, the gold has a slightly creamier look; however, if they're not right next to each other I think anyone would find it hard to tell which it is.
  
  

  The top ring here is sterling silver, and the bottom one palladium. You can see the difference in color: the silver is much whiter, while the palladium- a member of the platinum family- is grayer and looks more like platinum.

  
  
  
• Silver: Although silver is less dense and more susceptible to wear than most gold alloys, it has a lovely white color and can be a very practical choice for many things. Since it is both cheaper per ounce, AND less dense than gold or the platinum family metals, it can be very cost-effective for a design- especially one that will not see a lot of wear, or which is substantial enough to withstand wear. I love silver, and do a lot of work with it. There are various kinds of silver in common use.
• Fine Silver: this is pure- 99.9%- silver. It has a lovely white color and is somewhat less prone to tarnish than sterling is. It does have drawbacks, though- it's very soft compared to sterling, which means it dents, wears out, and otherwise does not withstand hard wear particularly well. This is especially relevant with all the work that's being done with PMC and Art Clay- while these are amazing products and allow wonderful work to be done- that work is even less sturdy than fabricated pieces made of fine silver mill products, since the firing process leads to porosity in the PMC/Art Clay (think of it as a metal foam, and you won't be far off). Keep this in mind if you look at rings, in particular, made of PMC/Art Clay fine silver. Most traditional metalsmiths may use fine silver for a bezel on a delicate stone, but not to fabriacate an entire ring or bracelet.
• Sterling silver: This is legally 92.5% silver, and the rest can be anything. As I tell people, it could be broccoli if one could figure out a way to make the mix stable! In good-quality sterling, the rest is copper, and that makes a pretty but sturdy, white metal that's useful for many things. It does tarnish due to the copper.
• Argentium sterling silver: This is a legal sterling (92.5% silver) that replaces some of the copper with germanium. Besides the benefits to its working qualities that I love, it has 2 significant benefits for jewelry. First, it is very slow to tarnish. Second, it can be hardened to make it as hard as 14k palladium white gold, which can make it a reasonable choice for rings that will get a lot of wear. In general, I prefer to make rings out of Argentium, since I know they hold up better.
  
  

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