It's a common question. The answer depends on the purpose. Is 18k being compared to 24k for jewelry and fashion purposes? Is it for metal plating car accessories? Is it for medical devices? Is it for electronics applications?
We posted a poll online and here are a few opinions:
I’m a jewelry historian/curator and author
The answer depends on what you are trying to accomplish with the design. If you are looking for a warmer, sunnier appearance then you would want 18k gold plating—this gives the piece the look of fine jewelry in the same caratage. 14k gold plating is used to give a golden sheen jewelry—remember the amount of gold used for plating is commonly negligible so that this point is more about appearance and design, rather than value.
Better sterling-based pieces are often plated in 18k to compete with fine 18k or even 14k gold jewelry. In my opinion, 18k gold plating is more convincing in terms giving the piece a more luxe look, while 14k gold plating can look lighter or whiter than fine jewelry crafted in 14k gold.
A geologist, environmental engineer and Caltech graduate, Addison's interest in the mesmerizing and beautiful results of earth's geological processes began in her elementary school's environmental club.
Personally, if I had to choose between an 18k gold plated item and a 24k gold plated item, I'd go for the 18k. The gold plating on either piece would wear off quickly, but the 24k gold plating has a higher gold content and a slightly higher price. However, I'd prefer gold filled jewelry to gold plated. Gold filled jewelry has a higher gold content, at least 5%, and won't wear off over time. That means you're paying for something that will last.
The 18K gold plating contains 75% of pure gold mixed with other metals for better hardness and strength, whereas the 24K gold plating is 100% pure gold. However, 24K gold is usually not used in jewelry making as it is very soft and vulnerable to damage. It is great for investment purpose but if you are looking for jewelry, 18K gold plating is better than 24K plating as it makes the jewellery durable.
Not everyone can afford the cost of solid gold items and may go with gold plating. The thing to be aware with gold plating is that it will not last forever and will eventually need to be replated. This is because gold plating a very thin layer of real gold that adheres to another metal (steel or sometimes silver).
24k is considered pure gold and is a very soft gold. Because of this, 24k gold is very rarely used in jewelry. However, since you are just plating an item rather than solid gold, you will not have the durability issue of the item bending or warping, but will still scratch off. Additionally, 24k gold has a much more yellow color than 18k Gold.
Most jewelers in the United States use 14k or 18k Gold because its more durable and the color is now what the average person thinks of for the color of gold. So if your piece is 24k and big, it will look very yellow compared to other jewelry and maybe hard to match. Lastly, because as I mention it will wear off and need to be replated, it is easier to replate 18k gold rather than 24k Gold.
My recommendation would be to do 18k because its more common and matches what most people think of for gold jewelry.