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"K18 Hard" that is thin yet resistant to bending


cobaco's jewelry features delicate items with a ring width of about 1mm. The reason we can deliver items that can be worn without hesitation in daily life, even with delicate designs, is because of the encounter with K18 Hard, a gold that is difficult to bend.


First, about K18

Pure gold (100% gold) is expressed as K24. K18 refers to the base metal containing 75% gold. The remaining 25% varies depending on the color, but typically includes silver or copper. By mixing these, the strength of soft gold is increased.

About K18 Hard|cobaco


The secret of strength lies in the remaining 25%

The gold content of K18 Hard is the same as K18, 75%. The remaining 25% includes components that strengthen gold, such as platinum and palladium.

Although the exact components are the trade secret of the metalworker, thanks to them, even delicate jewelry with a 1mm ring width can be worn with peace of mind every day.

About K18 Hard|cobaco

In fact, when we tried to bend a sample ring made of K18 Hard, it was so hard that it did not budge even with a little force applied.

However, despite being difficult to bend, it is still K18. If strong force is intentionally applied, it will bend, and it remains a delicate material. Please handle it with care.


We wore it for over a year

We actually wore it for over a year to see how much it would not bend in everyday life and if it is truly scratch-resistant. The item we wore was "tamago ring/narrow".

About K18 Hard|cobaco

We cooked almost every day, did laundry, cleaned, all while wearing the ring (without wearing gloves each time). We bought several days' worth of groceries at the supermarket, carried heavy items like cases of water and rice, and even transported heavy fixtures for events.


Doesn't bend, doesn't scratch

So, what were the results of the year-long experiment? First, take a look at the photos.

About K18 Hard|cobaco

The ring in the middle is the one we wore for a year. The one on the right is a brand new identical ring (different size), and the one on the left is a new matte version.

While the shine has diminished compared to the new one, there was no distortion, deformation, or discoloration. There are some fine scratches here and there, but they are hardly noticeable to the naked eye.

With regular K18, many more fine scratches would be visible, and the appearance would noticeably dull over time. After wearing K18 Hard for a year, we found that it is less prone to scratches.

*K18 Hard is still "K18." There is still a possibility of deformation. Even if used in the same way, it may bend depending on the load, and fine scratches may occur. Also, individuals may perceive fine scratches differently. Please consider these results as a reference.

*Some rings are not made with K18 Hard. Please check the material on each item page.