A ring for life together. Why MITUBACI chooses only "K18 (18K gold)"

When visiting jewelry shops and accessory stores, you increasingly see displays such as "K18," "K10," and "K5." We receive more and more questions from customers shopping for gold jewelry, such as "They all look like the same gold color, but what's the difference?" and "K10 and K5 are more affordable, but should I choose K18 or one of these?"

All gold jewelry created at MITUBACI is made exclusively from "K18 (18-karat gold)". We do not handle lower purity golds such as K10 or K5.

This is not simply because it is an expensive material, but because as a handmade ring workshop and jewelry brand that walks alongside our customers throughout their long lives, we have important commitments that we cannot compromise on.

This time, we will provide a detailed and careful explanation from the basic knowledge of gold as a material, to the reasons why MITUBACI continues to focus exclusively on K18, and the points for enjoying your rings as lifetime pieces for many years to come.

What is "K (Karat)" in the first place? Basic knowledge of gold purity

The "K" in the notation of gold jewelry stands for "Karat," which represents the "purity of gold" - indicating what percentage of gold is contained within the product.

It is a different unit from the "Carat" used to express the weight of diamonds and other gemstones. Gold purity is expressed on a scale of 24 parts, which is the worldwide standard. In other words, pure gold with 100% purity is expressed as "K24".

Using this as a standard, calculating the percentage of gold contained in the main types of gold yields the following:

・K24 (24-karat gold): Gold content 100% (pure gold)

・K18 (18-karat gold): Gold content 75% (18/24)

・K10 (10-karat gold): Gold content approximately 41.7% (10/24)

・K5 (5-karat gold): Gold content approximately 20.8% (5/24)

When arranged in numbers like this, you can see there is a significant difference. K18 is made up of three-quarters (75%) pure gold, but with K10 and K5, metals other than gold account for more than half of the total composition.

The non-gold portion is made up of a mixture of metals such as copper, silver, and palladium. These are called alloy metals (warigane). K10 and K5 have the advantage of being able to lower the price by reducing the proportion of gold, but at the same time they have the characteristic that the properties of metals other than gold become more pronounced.

Four reasons why MITUBACI continues to focus exclusively on "K18"

The reason we do not handle K10 or K5 and create only with K18 stems from our "responsibility to our customers' futures" gained through years of jewelry creation and maintenance experience. We will explain the four specific reasons.

1. Because it is unlikely to cause allergies and can be worn every day with peace of mind

Gold (yellow metal) is a metal with extremely stable properties. It is unlikely to deteriorate when exposed to sweat or air, and is a representative precious metal that is unlikely to cause metal allergies.

However, when the proportion of alloy metals (copper, nickel, etc.) increases as with K10 and K5, the metal components are more likely to dissolve when reacting with sweat and sebum, increasing the risk of skin trouble and metal allergies.

Wedding rings and special rings handmade at the workshop touch the skin every day for many years - for decades. Considering those with sensitive skin or potential changes in skin in the future, we choose K18 with high gold purity to ensure everyone can wear our pieces with confidence.

2. Because it resists discoloration and maintains beautiful luster with depth even as time passes

Pure gold does not discolor, but alloy metals such as copper and silver oxidize and discolor when reacting with oxygen, sulfur, sweat, and moisture in the air.

K10 and K5, having more alloy metals, may gradually become darkened or turn reddish as they are stored long-term or worn daily. In contrast, K18, being 75% pure gold, is highly resistant to discoloration and maintains the beautiful golden shine characteristic of gold for many years to come.

The major appeal of K18 is that you can enjoy unchanged beauty not just in the immediate term, but 5 years from now, 10 years from now, and beyond.

3. Because it has the durability for craftsmen to beautifully repair it repeatedly

MITUBACI is a workshop where our customers can handcraft their own rings. The one-of-a-kind ring created with care grows in sentimental value as you walk through life with it.

However, over the course of a long life, body shape changes, children grow, and finger size may vary with the seasons. In such cases, aftercare services such as ring resizing and re-polishing become necessary.

K10 and K5, which contain a high proportion of alloy metals, have properties that make the metal itself very hard and brittle. Therefore, when resizing a ring by cutting, expanding, or shrinking it, there is a high risk of cracks forming in the metal or welding marks becoming visible.

On the other hand, K18 combines appropriate strength with malleability (ductility).

Through the skilled hands of professional artisans specializing in metal engraving, resizing and re-polishing can be performed beautifully even after many years. K18 is an essential material to continue maintaining your handmade, treasured ring in perfect condition decades into the future.

4. It has "reliable asset value" that transcends time and never loses its worth

Gold is a metal with universal value recognized worldwide. Despite recent global circumstances and economic changes, the asset value of gold continues to be highly appreciated.

K18 is firmly recognized internationally as a "high-quality precious metal," and owning it itself holds certain value. When passing rings down to your children or future generations in the future, an 18-karat gold ring can be proudly passed on as a valuable treasure.

The charm of K18 colored gold available at MITUBACI

When you hear "18-karat gold," many people may think of dazzling yellow gold, but by adjusting the alloy composition ratio, we can create various beautiful color variations.

At MITUBACI, while maintaining the superior quality of K18 throughout, we offer a diverse palette of colors that suit our customers' preferences and skin tones.

・K18 Yellow Gold: A golden hue with classic brilliance and elegance.

・K18 Pink Gold: A warm-toned color with good skin compatibility that imparts a soft and gentle impression.

・K18 White Gold: Often called blue gold, this is a gold with a brilliant impression.

・K18 Champagne Gold: A natural color that seamlessly blends with the skin, with an exquisite balance of yellow and silver tones.

Whichever color you choose, all contain 75% pure gold in 18-karat quality, so the depth of color and smoothness of touch are truly exceptional. At our workshop, you can handle actual sample rings and experience the difference in color and texture when placed against your skin.

The "tactile sensation of genuine materials" that can only be felt through hands-on creation

At MITUBACI's workshop, you can experience the creation process where you yourself use a hammer to tap the ring, stamp engravings, and carefully polish the surface.

During this creation process, the difference in materials is clearly evident in the "tactile feedback" when striking the metal and the "beauty of the hammer marks."

K18 provides a uniquely pleasant tactile sensation when struck with a hammer—neither too hard nor too soft. As you tap it, the metal's density increases, making the ring more resistant to scratches and stronger. The time spent using craftsman's tools with your own strength to impart patterns and form to authentic K18 gold is a luxurious and special experience found nowhere else.

A ring you have created from scratch with your own hands generates far more attachment than purchasing a ready-made product. That is precisely why we want to provide you with the finest K18, a material worthy of a lifetime of love.

Tips from our craftsmen! Daily care for K18 rings and frequently asked questions

We introduce frequently asked questions from our customers and simple daily care methods you can do at home.

By having the correct knowledge, you can keep your K18 ring beautiful and pristine for much longer.

Q1. How should I care for my ring on a daily basis?

After wearing, the basic step is to gently wipe away sweat and oils using a soft cloth or eyeglass cleaning cloth. If you notice oils or tarnish, dissolve a small amount of neutral detergent (such as dish soap) in lukewarm water and gently wash with a soft brush (such as a toothbrush), and the brilliance will be restored as if it were new. After rinsing, make sure to wipe away moisture thoroughly with a soft cloth.

Q2. 温泉や海水浴のときは外したほうがよいですか？

K18は変色に強い素材のため、基本的には温泉に入っても大丈夫です。まれに温泉に含まれる成分、特に硫黄や、海水に含まれる塩分、プールで使われる塩素などに反応して、表面がうっすらと変色してしまう可能性がございます。もし変色してしまったとしても、表面を磨くことで色は戻りますので、ご安心ください。

Q3. 日常生活でキズがついてしまった場合はどうすればいいですか？

毎日身に着けていると、どうしても生活の中で細かい小傷がついていきます。しかし、このキズもまた、おふたりで過ごした時間の証であり、指輪に味わいを与えてくれるもの、という考えもあります。もし「一度ピカピカの状態に戻したい」と思われる場合でも、ご安心ください。MITUBACIでは職人による磨き直し（仕上げ直し）のアフターサービスを行っております。K18であれば、何度磨き直しても美しく新品のような輝きを取り戻すことが可能です。

まとめ：未来の自分やおふたりへ贈る、妥協のない選択

ジュエリーを選ぶ際、価格やデザインはもちろん大切な要素です。しかし、手作り指輪のように「一生の思い出」としてずっと身に着け続けるものだからこそ、私たちは素材の品質や耐久性、将来のメンテナンス性に妥協したくありません。

低純度のK10やK5にはない、K18だからこその「肌への優しさ」「変色しにくさ」「サイズ直しのしやすさ」、そして「普遍的な価値」。これらはすべて、数年後、数十年後のお客様の満足感と安心感につながっています。

「この素材で作って本当に良かった」「10年経った今も、変わらず美しい」。お客様にそう思っていただけるよう、MITUBACIはこれからもK18という最高の素材にこだわり、心を込めた指輪作りのお手伝いを続けてまいります。

MITUBACIの工房では、K18のサンプルリングを実際に手に取り、その重厚感や深みのある輝きをお確かめいただけます。ご質問や気になる点がございましたら、いつでもお気軽にスタッフや職人へお声がけくださいませ。