About Precious Metals

Gold, Silver, Argentium Silver, Platinum, Palladium are precious metals.
Gold – Gold is a highly sought-after rare metallic element. When it is alloyed with other metals the term carat/karat/kt is used to indicate the amount of gold present. The purity or fineness of gold in the jewelry is indicated by its karat number.  Pure gold is (24/24ths) 24kt gold.. 18kt gold is (18/24ths) gold and (6/24ths) other metals. Only 24kt gold is 100% pure gold. Is a very soft metal when it is pure 24kt.
It is often alloyed with silver, palladium and copper metals to make it harder though this lessens the value.
https://en.wikipedia.org/wiki/Gold
Silver – Silver was once thought more precious than gold.
It is a very soft metal and is often mixed with an alloy like copper. To be sterling silver, the metal is made up of 92.5% silver and 7.5% copper.
Silver tarnishes after exposure to contaminants such as ozone. The best way to deal with this is use silver dip or wipe with a polishing cloth.
https://en.wikipedia.org/wiki/Silver
Difference between sterling, and Argentium sterling silver?
Sterling silver is a silver alloy of 92.5% silver and 7.5% copper. The copper makes the silver harder and more durable but also causes the silver to tarnish over time.
Argentium sterling silver – is also a silver alloy like sterling silver. Argentium sterling silver is at least 92.5% silver and a combination of copper and germanium, Argentium sterling silver does not tarnish.

Argentium’s superior purity ensures that finished items are of the highest quality. Customers are asked
to look for the Argentium ‘flying unicorn’ mark on jewellery and silverware as a guarantee that items
have been produced with ‘the finest silver’ in the world.
Platinum (PT) – Platinum is more precious than gold, it is a very strong dense metal that never corrodes. In its pure form it is harder than gold and silver. Platinum’s wear and tarnish resistance characteristics are well suited for making fine jewelry.
For jewelry it is alloyed with 5% of other metals, usually Iridium (another even rarer metal in the platinum family) to make it more workable.
It is a rare grayish white metal.
https://en.wikipedia.org/wiki/Platinum-iridium_alloy
Palladium (Pd) – Palladium is an element belonging to the platinum group of metals, Palladium is steel-white in color, except in powder form, when it appears black. Palladium resists tarnishing in air. Most palladium is used for catalytic converters in the automobile industry, also used in dentistry and now in jewelry due to its naturally white properties. Palladium is one of three most used metals which can be alloyed with gold to produce white gold. Palladium-gold is a much more expensive alloy than nickel-gold but is hypoallergenic and holds its white color better.

The primary use of gold / palladium alloys is in jewellery. The alloy is more commonly known as white gold and is an alternative to platinum. Gold / nickel alloys are also used as white gold. In both cases some other metals may be present in small amounts such as silver, zinc and copper.

The cost of palladium white golds are greater then that for nickel white golds due to palladium higher cost and more difficult processing. Palladium white golds are also softer and more ductile compared to nickel white golds. In both cases it is not possible to have white gold with a purity greater than 21 carat.

https://en.wikipedia.org/wiki/Palladium

Metal Allergies – If wearing certain jewelry causes localized areas of skin to become itchy, red and/or swollen this can indicate an allergic reaction to the metals in jewelry.Nickel is the most common culprit; if a 9kt gold earring, bracelet, necklace or ring is causing a reaction, it’s the nickel in the gold NOT the gold itself causing the problem. Women are more commonly affected by a nickel allergy than men. People rarely have a reaction to pure gold (24kt), platinum or titanium.

There is a risk of allergic reactions with sterling silver too.

Nickel-Free Metals
Another option is to avoid base-metal alloys entirely, and instead use elemental and precious metals in your custom jewelry. The following options are all nickel free.

Sterling silver is an alloy, but does not contain any nickel, so is wearable by most segments of the population. Sterling is sometimes stamped .925, because it’s made of at least 92.5% pure silver. Typically the remaining 7.5% consists of copper.

Tarnish-resistant Argentium sterling silver is 1.2% germanium, 6.3% copper and 92.5% silver.

Niobium is an element and is therefore not mixed with any other metals. It is naturally nickel free and very resistant to corrosion. Niobium comes in a wide variety of anodized (non-plated) colors.

Titanium is also an element and thus naturally nickel free. Like niobium, it’s highly resistant to corrosion. Because of this, titanium is frequently used in medical implants and is a good choice for earring findings.

14k White Gold is commonly made of the following materials: 58% pure gold, 25% pure silver, and 17% pure copper. Gold can be alloyed with other metals, too. Be aware that white gold commonly contains nickel (added for both color and strength).

The term hypoallergenic was made up in the 1950’s as part of an advertising campaign and has since been adopted to indicate that the metal used has a diminished potential for causing an allergic reaction.

Tarnishing – Some, not all, metals tarnish. The discoloration occurs when the metal is able to react with or be attacked by something that can make a chemical compound with the underlying metal. Silver can react with oxygen or sulphur compounds to form a brownish-to-black tarnish film. This is due to the formation of oxides (An oxide is a chemical compound containing at least one oxygen atom as well as at least one other element) and/or sulphides (a compound of sulphur and an element that has a more positive electric charge) on the metal surface. Because of the small particle size, the oxide/sulphide particles on the surface appear black, so the metal loses its luster. Pure gold is resistant to such reactions however lower karat golds are all alloys of gold with other metals and as such can tarnish. Wherever it occurs, tarnish almost always looks very different from the original polished metal. Tarnish is removed either by employing another chemical reaction to dissolve the tarnished surface or by using a mild abrasive to actually polish away the discolored compound on the metal to expose the underlying metal again. Ordinarily, such cleaning processes remove very little of the original metal.

Metal hardness – Titanium is given a 6 on the Mohs Hardness Scale, a scale used to rank materials by their scratch resistance. In comparison, gold is a 3 rating, and platinum is generally given a rating of 4 to 4.5. So, titanium rings are a few times harder than their precious metal counterparts.