Underglaze vs Overglaze: What’s the Difference?
If you are new to pottery and ceramics, the world of glazing can feel overwhelming. There are shelves full of bottles and jars at your local pottery supplier, each promising different effects, finishes, and application methods. Two terms you will encounter very quickly are underglaze and overglaze – and while they might sound self-explanatory, the differences between them go well beyond simply where they are applied on a pot.
Understanding how each type works, when to use one over the other, and how they interact with firing temperatures will help you make informed decisions at every stage of your making process. This guide breaks it all down clearly, with practical advice suited to beginners working in home studios, community pottery classes, and shared kiln spaces across the UK.
The Basics: What Are Glazes?
Before distinguishing between underglaze and overglaze, it helps to understand what a glaze actually is. In its simplest form, a glaze is a glassy coating that is fused onto the surface of clay through heat. It typically contains silica (which forms the glass), alumina (which stabilises it), and a flux (which lowers the melting point). When fired in a kiln, these ingredients melt together and bond permanently to the clay body beneath.
Glazes serve two purposes: functional and decorative. Functionally, they seal porous clay, making vessels food-safe and waterproof. Decoratively, they provide colour, texture, and surface interest. Both underglaze and overglaze contribute to that decorative dimension, but they do so at different stages of the firing process and with very different characteristics.
What Is Underglaze?
Underglaze is a colourant applied to clay before a transparent or translucent glaze is applied on top. It can be used on greenware (unfired clay), bisqueware (clay that has been through its first firing), or even on raw clay, depending on the specific product. Once the underglaze is applied and dried, a layer of clear or transparent glaze is brushed, dipped, or poured over it, and the piece is then fired to its final temperature.
During the glaze firing, the underglaze colours fuse into the surface of the clay and are sealed beneath the glassy overcoat. This gives the finished piece a smooth, even appearance, with the colours locked in safely beneath the surface. Because of this, underglazes are extremely stable and predictable – what you paint on tends to look very close to what you get out of the kiln, which makes them particularly beginner-friendly.
In the UK, popular underglaze ranges include Amaco Velvets, widely stocked by suppliers such as Bath Potters’ Supplies in Bath and Scarva Pottery Supplies in Northern Ireland. Spectrum Underglazes and products from Potterycrafts in Stoke-on-Trent – the heartland of British ceramics – are also commonly used in studios and colleges across England.
What Is Overglaze?
Overglaze, by contrast, is applied after a piece has already been glaze-fired. It sits on top of the existing glaze surface rather than beneath it. Overglazes include a range of products: china paints (also called enamel paints), lustres, and gilding preparations. They are fired at much lower temperatures than standard glazes – typically between 700°C and 850°C – because at this point the goal is simply to fuse the overglaze decoration onto the already-vitrified surface below, not to melt an entirely new glassy layer.
Overglazes have a long history in British ceramics. The exquisite hand-painted decoration on Royal Crown Derby china, the delicate gilding on Wedgwood pieces, and the vibrant enamel work on Portmeirion pottery all make use of overglaze techniques. For studio potters and beginners, lustres in particular have grown in popularity over recent years, giving pieces a metallic or iridescent sheen that simply cannot be achieved with standard underglaze or glaze alone.
One important consideration with overglazes: because they sit on the surface rather than being sealed beneath a glaze, some – particularly certain lustres and gold preparations – are not food-safe and should not be used on the interior of functional ware such as mugs or bowls. Always check the manufacturer’s guidance and, where relevant, consult current UK food contact materials regulations before using any ceramic product for food or drink.
Key Differences at a Glance
The table below summarises the most important differences between underglaze and overglaze to help you decide which is right for your project.
| Feature | Underglaze | Overglaze |
|---|---|---|
| Application stage | Before the glaze firing – on greenware or bisqueware | After the glaze firing – on an already-fired glaze surface |
| Firing temperature | Fired at the same temperature as the main glaze (e.g. 1060°C-1280°C) | Fired at a lower temperature, typically 700°C-850°C |
| Finish | Sealed beneath glaze; smooth, stable, matte or glossy depending on top glaze | Sits on the surface; can be metallic, iridescent, or enamel-bright |
| Food safety | Generally food-safe when used correctly with a suitable clear glaze | Variable – lustres and some enamels are not food-safe; always check manufacturer data |
| Beginner-friendliness | High – colours are predictable and easy to apply with a brush | Moderate – requires a second firing and careful handling of specialist materials |
How to Apply Underglaze: A Step-by-Step Guide
Applying underglaze is one of the most accessible decorating techniques in ceramics. Here is a straightforward process to follow if you are working with commercial underglaze on bisqueware, which is the most common approach for beginners.
- Prepare your bisqueware. Make sure your piece has been bisque-fired and is clean and dust-free. Wipe it gently with a damp sponge if needed, then allow it to dry completely.
- Stir or shake your underglaze. Commercial underglazes can settle in the bottle. Give them a thorough mix before use to ensure an even colour consistency.
- Apply your first coat. Use a soft brush to apply a thin, even coat of underglaze to your piece. Work in one direction where possible to avoid streaking. At this stage, the colour will look faint – this is normal.
- Allow to dry between coats. Underglaze dries relatively quickly. Wait until the surface is no longer shiny before applying the next coat.
- Apply two to three coats in total. Most underglazes require at least two coats for full, opaque colour. Three coats will give the richest result. Each coat should be applied in a slightly different direction to build up even coverage.
- Clean up any unwanted marks. Use a damp sponge or a fine-tipped brush dipped in water to remove any underglaze from areas where you do not want it, such as the base of the pot.
- Apply a clear or transparent glaze over the top. Once your underglaze is fully dry, apply your chosen clear glaze using the method appropriate to your studio setup – brushing, dipping, or pouring. Avoid disturbing the underglaze layer beneath.
- Fire to the recommended temperature. Load your piece into the kiln and fire according to the manufacturer’s instructions for both the underglaze and the clear glaze you have used.
Working with Overglaze: Practical Tips for Beginners
Overglazes require a slightly different approach and a bit more patience. Here are some practical points to keep in mind before you start.
- Start with lustres if you are new to overglazes. Lustres come in small bottles and are applied thinly with a soft brush directly onto a fired, glossy glaze surface. They are widely available from UK suppliers such as Potclays in Stoke-on-Trent or UK Pottery Supplies online, and give striking results with relatively little experience required.
- Work in a well-ventilated space. Many overglaze products, particularly lustres, contain solvents that produce fumes during application and firing. Always work with adequate ventilation and follow the safety data sheet provided by the manufacturer.
- Apply thinly and evenly. With lustres especially, less is more. A thick application can cause crawling, pitting, or an uneven metallic finish. One thin, even coat is almost always sufficient.
- Clean your brushes immediately after use. Lustre and enamel products can damage brushes if left to dry in the bristles. Use the appropriate solvent – usually available from the same supplier – to clean tools straight after use.
- Fire in a clean kiln. Overglaze firings are sensitive to contamination. Smoke, residue from previous firings, or even dust can affect the final surface. If you share a kiln in a community studio, check with the studio manager about their recommended procedure for overglaze firings.
- Keep records of your firings. Because overglaze results can vary between kilns and firing schedules, keeping a log of what you used, how thickly you applied it, and what temperature you fired to will help you repeat successes and avoid repeating mistakes.
Can You Use Underglaze and Overglaze Together?
Yes – and many experienced potters do exactly that. A common approach is to decorate a piece with underglaze for the main design, apply a clear glaze on top, fire it to the full glaze temperature, and then add lustre or gold overglaze details in a subsequent lower-temperature firing. This layered approach allows for a wide range of effects: the stable, painterly quality of underglaze combined with the drama of metallic or iridescent overglaze accents.
If you attend a pottery class or work in a shared studio in the UK, it is worth asking your tutor or studio manager whether they have experience running overglaze firings. Not all community studios offer this service as standard, since it requires a separate firing cycle. Some studios in larger cities, particularly London, Manchester, and Edinburgh, have expanded their facilities in recent years to accommodate overglaze work as interest in decorative ceramics has grown.
Choosing Between the Two: What Should Beginners Prioritise?
For most beginners, underglaze is the natural starting point. It is forgiving, versatile, and widely available at a sensible price point. You can use it to paint intricate patterns, block-colour geometric designs, or loose illustrative motifs. The colours are reliable, and the technique integrates seamlessly into standard bisque-and-glaze workflows that most pottery
classes and studios teach. The glaze layer applied over the top seals and protects the decoration, meaning finished pieces are durable enough for everyday functional use — cups, plates, and bowls included.
Overglaze, by contrast, rewards patience and a degree of prior experience. Because it is applied to an already-fired glaze surface, any mistakes cannot simply be wiped away and reworked in the same forgiving manner as wet clay allows. The firing temperatures are lower, which can make kiln scheduling slightly more straightforward in shared studio environments, but the enamels and lustres themselves require a confident, decisive hand. Beginners who are drawn to the jewel-bright colours of overglaze work are best advised to develop their underglaze skills first, building an understanding of how pigments behave and how brush control translates into finished line quality.
That said, there is no rigid rule. Some learners find that overglaze painting, particularly with simple lustre washes rather than detailed enamel work, clicks intuitively from the start. Local adult education courses in cities such as Bristol, Sheffield, and Glasgow increasingly offer taster sessions covering both approaches side by side, which gives newcomers a practical basis on which to make an informed choice rather than relying on received wisdom alone.
Conclusion
Underglaze and overglaze are complementary techniques rather than competing ones, each suited to different aims, aesthetics, and stages of a maker’s development. Underglaze offers accessibility, integration with standard studio workflows, and reliable colour results that hold up well in functional ware. Overglaze opens the door to surface qualities — metallic lustres, translucent enamels, fine painted detail — that no amount of underglaze work can replicate. Understanding the distinction between the two, and knowing which to reach for at a given moment, is one of the more useful judgements a potter working in the British studio tradition can develop over time.
