In the late 1950's the constructed peg head was introduced. It took advantage of the stiffness and spring tension of nickel which was the metal most commonly used to make white gold. The die struck sheet meant that the metal was the same width for the prongs but the pieces were shaped to fit together to make the four or six prongs of the head. The extra density of the sheet and high nickel content allowed the diamond to be suspended without a brace or side walls and was instantly popular. The old tiffany was cast in the shank and had a narrowing base but with thicker walls. This new peg head had a less limiting view and was much more adaptable to modern designs. It became known as the new tiffany. By the late 1960's the die struck head was the most common head used and was available in both 4 prong and six prong. Four prong was the most common as people enjoyed viewing the pavilion of the diamond and it made it very easy to keep clean which helped the brilliance of the diamonds.
In the 1970's more and more people began having problems with prongs snapping and stones being lost. It seemed a greater problem in California so a popular magazine studied the problem and estimated it was the chlorine especially in swimming pools and diaper buckets that was the problem. They suggested a solution. Use six prongs so that when a prong snapped it would be repaired without losing the stone. High end stores began using platinum heads and tipping the prongs with platinum during a repair. The platinum prongs did not have the spring tension or the stiffness so they twisted and without the spring tension stones loosened more often. Some went back to the cast head with the widening prong base but it did not become popular. The tipping with platinum was a bad idea as the platinum had to be applied with solder which was attacked by chlorine and sheared off where it was soldered.
In 1990 more people were becoming unable to wear nickel white gold. They would get a rash. The problem is still growing to this day. In 1979 about 4.5% of the population had a nickel sensitivity. By 1990 the percentage was over 11%. (I've read estimates of 14 to 16% today.) Platinum was now becoming popular as more people could afford it and luxury items were in vogue. It was sold on it's purity, durability and natural color of white (though it was being rhodium plated just like white gold). Platinum prices kept rising and people retreated back to white gold. Because of rhodium they now looked the same in the showcase. In an attempt to make Platinum more affordable, a new alloy was used to make platinum casting more exacting and less expensive because it saved considerably on the long cleanup time required for platinum. Cobalt made the metal flow better and with greater detail and less flashing. However it wears more similar to gold than the traditional platinum which is is known for it's durability. Because once platinum is 950 parts per thousand pure the alloy does not have to be disclosed, many retailers do not know which alloy they are selling, sizing or repairing.
By the year 2000 it was a full mix without a map. Different manufacturers alloyed their white gold with various percentages of nickle. Some wanted to be known as the whiter white gold and used more nickel some were afraid there would be laws passed unless the amount of nickel was reduced dramatically so their metal was quite a bit yellower. England banned nickel in jewelry and clothing outright in 2004. Everybody thickened the amount of rhodium plating that was on their jewelry so they all looked the same in the showcases. Finally a whiteness chart became available but few wanted to be rated.
Currently gold prices are hitting new highs with gold over $1800 per oz. This makes the platinum group of metals more appealing again. Palladium, which was popular for it's whiteness and rarity before World War two at which time it was placed aside as a strategic metal, is back in popularity because of it's reasonable price. It's lightness and softness make it fine for heavier and engraved designs, and it is inert and hypoallergenic as well as rare and precious. Platinum is closer to gold in price than it has been for quite a while and is being revitalized by new denser castings and the cobalt alloy which makes it stiffer for more delicate designs. As a natural white metal that is hypoallergenic it's new more affordable styles are capturing an important place in the market.