Frequently Asked Questions

At your service
Our diamond consultants are standing by to help you find that specific diamond piece you're looking for. They take all your wishes into account, including your budget.

General Information

What is Royal Coster Diamonds?
Royal Coster Diamonds is a Dutch diamond polishing company. It is one of the oldest diamond polishing companies still operating in the Netherlands. With nearly 200 years of history, Royal Coster is responsible for many historical masterpieces. Royal Coster has made jewelery for, among others, Prince Napoleon and Empress Sisi. In 1852, Royal Coster's craftsmen were selected by Queen Victoria to re-polish the world's largest diamond, the Koh-I-Noor (Mountain of Light).

What are your opening hours?
We are open from 9 AM to 5 PM, seven days a week, including Sundays. If you want to make an appointment outside regular opening hours, please contact us on +31(0)20 305 5555.

Where are you located?
Paulus Potterstraat 2- 6
1071 CZ, Amsterdam
The Netherlands

Are you focused on dutch visitors or international visitors?
Royal Coster Diamonds receives visitors from all over the world and focuses on all international markets. Royal Coster Diamonds also delivers its jewelery worldwide.

Who is working there?
Royal Coster Diamonds has many specialists in service from the world of jewelry. Our sales staff has years of experience and specialize in gemstones, jewelry and of course diamonds. Our craftsmen are carefully selected and are some of the best diamond polishers in the world.

Visiting Royal Coster Diamonds

I am a tour leader, guide or work at a tour operator. Where can I find more information?
You can always contact our travel advisor for a tailor-made program or advice. For more information please email us at tours@royalcoster.com.

Is there a way to combine my trip to Royal Coster with other activities in Amsterdam?
Royal Coster is in close contact with other attractions in Amsterdam. Due to the close proximity of the Rijksmuseum and Moco, for example, it is very easy to combine a tour.

Which tours, experiences and/or workshops do you offer?
Royal Coster offers various tours, experiences and workshops. Coster is also open to events. Examples of tours are the guided tours through the grinding factory, the Royal Experience or Sparkling Holland. For all the experiences you can go to our tours page: https://www.royalcoster.com/collections/tours-and-workshops

How can i contact you to book a our or describe my product wishes?
Royal Coster can be reached daily by phone from 09:00 - 17:00
on +31 (0)20 305 5555. For extensive questions or bookings, it is best to email us at tours@royalcoster.com.

Do I need an appointment to visit you?
It is strongly recommended to make an appointment with Royal Coster in advance, so that we can tailor the experience to your wishes as much as possible.

About our diamonds

Are the diamonds you offer natural or lab grown?
All of the diamonds used by Royal Coster are 100% natural.

Are your diamonds certified?
All diamonds of Royal Coster are officially licensed

What are the 4 C’s?

1st C: Carat
Carat is the weight of a diamond. We use carat actually to express the weight of all gemstones. Carat comes from the French word Carob. Carobs are the seeds of the fruit of the carob tree. These seeds are distributed very evenly and universal weight. On seed weighs on average 0.2 grams. Carat indicates the weight of a diamond. But to make it easier for customers and dealers, the carats are divided into points. One carat is 0.2 grams and 100 points. Half a carat is 50 points and weighs 0.1 grams. A quarter carat is 0.05 grams and thus consists of 25 points, and so on. This point system makes it easier and clearer for both the seller and the buyer. The density of a diamond – the specific weight – is 3.2 gram per square centimeter.

2nd C: Colour
The color of a diamond is determined by using verification stones. These are diamonds in all different colors and gradations. Usually goes: the less color, the more valuable the diamond is. However, it is not like yellow(ish) colors are worthless. An example is a yellow stone that was recently sold at an auction for 8 million euros. Quite something for a polluted stone don’t you think? Below is a scale with the current and old names, that explains how a diamond is graded based on color and the absence of it. The closer to the start of the alphabet, the purer the stone.

3rd C: Clarity
A natural diamond is rarely without imperfections. It is a hallmark of Mother Nature to show that nothing is perfect. To evaluate a diamond’s clarity, we use a 10x magnifying glass. This is the tool everyone uses to have unity in the outcome. Under a microscope, you will always see impurities.

4th C: Cut
The Cut, or shape of a diamond is important to determine the quality of the polished diamond. The shape a diamond will become depends on the diamond quality and the amount of material loss in the process from rough to polished. A good diamond worker can cut a diamond in almost every shape imaginable. However, it is important that the cutter keeps the way the light reflects in mind. There are several preferred cuts: the brilliant, emerald, princess, marquise, pear, heart, oval, cushion, Asscher and baguette.