Diamond and Gemstone Buying Guide

Diamonds: The 4c's. This is a World recognised method for assessing the quality of a diamond. When choosing a diamond, it is good to know a little about the 4c’s so that you know what you are paying for. The price of diamonds fluctuate much like the gold price and usually due to demand for a certain cut or weight.

The 4 c’s are explained below. If you have any further questions, please do not hesitate to contact us.


The colour grading of a diamond is determined by how ‘colourless’ it is. The less colour in a diamond, the more desirable and valuable it is. The chart below is a rough guide to the grading of a diamond from D colour being colourless to S and below which have a yellow colour. Fancy colour diamonds are created when certain minerals are apparent in the Earth’s mantel where they are created. They come in a full array of striking colours including red, pink, purple, green and blue. The cost of fancy colour diamonds are determined by their rarity and are graded slightly differently than colourless stones.

diamond colour chart


The cut dictates how light disperses through the stone which determines how they sparkle. A well cut diamond reflects lots of light internally via the facets of the stone, dispersing light evenly through the table (the top).A shallow or wide cut stone will lose light through the bottom of the stone. Too deep or narrow and the light will be lost through the sides. Diamonds are graded on a scale of Excellent, Very Good, Good, Fair and Poor. An explanation of the cut will be stated on a diamond certificate.

diamond cut chart

Clarity (Quality)

Clarity is the description of a diamond's internal purity. Fewer imperfections in the stone will raise the price of the stone as flawless diamonds are fairly rare. There are many types of flaws in a diamond which can affect the way that light disperses through the stone. The chart below shows the definitions used for clarity grading…

diamond clarity chart

Carat (Size)

The weight of a diamond is measured in Carats. 100 points is equal to 1 carat in weight. 75 points is equal to 0.75ct or 3/4ct. One carat is equal to 0.2 of a gram. It is important to note that two diamonds can weigh the same but due to the difference in colour/clarity, the price can vary greatly. It is common, when a number of smaller diamonds are set together to give a total diamond weight.

diamond size chart

Diamond Certificates

At Purnell jewellery, we pride ourselves in sourcing the best diamonds to suit your budget. Diamonds that are used in our bespoke pieces will be GIA or IGI certified. Smaller diamonds will be graded at G/VS unless the design or budget of the piece requires another colour/clarity. We will always advise you of the colour and clarity so that you are fully aware of what you are paying for.

Diamond and Gemstone Shapes

Diamonds and Gemstones are cut in a wide variety of shapes. Here is a chart of the most popular shapes although proportions can vary.


Gemstones are available in a huge array of colours, types and shapes. At Purnell Jewellery we are happy to advise on the best gemstone for your commissioned piece during the design process. If required, we will provide a selection of gemstones for you to choose from along with a full description of the stones, prices and advise on how to choose the best item. With a vast knowledge of gemmology, our team are able to make sure that you receive the best stones to suit your budget. Please contact us if you have any queries.

Ring Sizing

Ring sizes are measured differently in different parts of the World. As we are a UK based company, we use sizing’s from A-Z+. To convert other measurements please use the following table...

pdfRing Sizing
Click below to download our ring sizing guide.

Download our ring sizing guide

pdfRing Conversion
Click below to download our ring conversion chart.

Download our ring conversion chart

Choosing A Ring Design

Ring Size: Ideally your partner’s finger size will be measured by a professional jeweller. However, this is not always possible, here are a few suggestions on how to obtain it...

If the above is not possible, print out the ring sizing guide provided on this website here or request a free ring sizer via our contact page. Once you ring is finished, if the ring does not fit, we will resize it for free within 30 days.

Design Guide

There are many different styles and settings available. Research the kind of design that you like. Look at how the stones are set. There are many types of settings for gemstones, our team will be able to advise you during the design process through sketches and images. We also have a variety of samples available to get the design process started.

Another thing to consider is your significant others style. Do they like classic or contemporary design? Would it be possible to take pictures of the style of jewellery that they choose to wear?

The metal type is also important. Does your partner have a preferred colour of metal (white, yellow, red), or type (gold, platinum, palladium, silver) and finally does your partner have any allergies to metal i.e nickel?

Also, we offer an engraving service to give your new item an extra special edge.

With this information, we will be able to create a unique piece of jewellery to cherish forever. During your initial design consultation we will work on the basis of the design and the budget available. We will then hand sketch our ideas for your approval. We aim to involve our clients in the design process of a piece of jewellery so that the perfect result can be achieved.

Jewellery making processes

Traditional methods: Although machinery may have made jewellery making a little easier over time, the basics have not changed for hundreds if not thousands of years. A jewellers workshop consists of a few staple pieces of equipment such as acid baths for cleaning, torches for soldering and heat work, rolling mills for metal work, motors for drilling etc and hand tools such as hammers and files. There are many processes in the production of a piece of jewellery such as wax casting, casting, polishing and setting. Each piece requires different methods depending on the design.

We are able to show you how your piece will be made in our onsite workshop during your design consultation.

Computer Aided Design: This is a fairly new method of jewellery manufacture. Jewellery designs are drawn on a computer program and when finished printed in wax and cast in the desired metal. This process enable very complicated designs to be produced at a fraction of the cost. A render can be produced for a customer approval which also gives a great idea of how the finished item will look. We will explain the manufacturing process in further detail during your design consultation.


Unique bespoke jewellery creations and repairs to suit any budget.

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Buying Guide

Read our helpful information guide before buying jewellery.

Professional Goldsmiths

Associate Fellow

Associate Fellow of the Institute of Professional Goldsmiths.


Designer/Craft Member

We are a member of the National Association of Goldsmiths.

Our Jewellery Services At A Glance

jewellery repairs


Unique, personalised jewellery to suit any budget.

jewellery valuations


Insurance approved professional jewellery valuations.

pearl bead stringing


Beautiful bead stringing for a range of gemstones.

ring sizing

Ring Sizing

Download our free printable ring sizing guide now.



We can make your old jewellery sparkle like new.