In the glaze vs underglaze comparison, glaze is a glass-forming coating applied as the final layer to protect and finish a piece, while underglaze is more like paint, used to add colour and decoration underneath that final glaze layer. They work together rather than competing, and most decorated pottery genuinely uses both.
New potters hear both terms thrown around constantly in a first class, glaze this, underglaze that, and it’s genuinely easy to walk away still unsure whether they do the same job. Here at Le Studio Art Space, clearing up glaze vs underglaze confusion is practically a rite of passage in an introductory class, so here’s a simple, honest breakdown of what each one actually does.
What Glaze Does
Glaze is a glass-forming coating, made mainly from silica, flux, and alumina, that melts in the kiln to form an actual glass layer over the surface of a piece. Once fired, that layer is what makes a pot waterproof, food safe, and resistant to staining, on top of giving it whatever colour and finish the glaze itself provides.
Because glaze forms a genuine glass surface, it’s typically the very last layer applied before the final firing. Anything underneath it, whether that’s bare clay, slip, or decoration, gets sealed beneath that glass once the piece comes out of the kiln, which is exactly why glaze functions as both a decorative and a protective layer at the same time.
Glaze comes in the full range of finishes and colours you’d expect, from clear and transparent through to deeply saturated solid colours, and in glossy, matte, or satin textures depending on the specific recipe. Whatever effect it’s designed for, its core job stays the same, forming that final protective glass coating.
Because it’s the layer that actually contacts food and drink on functional ware, glaze also carries the most direct food safety responsibility of the two. Choosing a glaze specifically labelled as food safe, and firing it correctly to its stated cone, is what makes a finished mug or bowl genuinely safe for daily use.
What Underglaze Does
Underglaze works more like a coloured paint or slip, applied directly to the clay surface to add colour, pattern, or fine detail before the final glaze goes on. It doesn’t melt into a glass layer the way glaze does, which means it holds detail, like brushwork, fine lines, or stamped patterns, far more precisely than glaze typically can.
This is really where underglaze earns its name and its purpose. Because it sits underneath the final glaze layer, it gives potters a way to add genuinely detailed imagery, lettering, or painted decoration that a thicker, glassier glaze would otherwise blur or obscure if applied directly to bare clay.
Underglaze is typically applied to either bone-dry greenware or bisque-fired pieces, and it comes in a huge range of colours, since it isn’t limited by the same melting and flow behaviour a functional glaze needs to manage. That range is part of why so much of the fine, detailed decoration you see on painted pottery is underglaze work rather than glaze itself.
Underglaze also layers and blends nicely with itself, similar to watercolour or gouache, which means potters can shade, gradient, or build up depth in a painted design well before any glaze even enters the picture. That flexibility is a big part of why illustrative and painterly pottery decoration relies so heavily on it.
When Each One Is Applied In The Process
Timing is where a lot of the glaze vs underglaze confusion actually comes from. Underglaze is generally applied earlier in the process, either to greenware before the first bisque firing, or directly onto bisqueware before the glaze firing, depending on the specific product and the studio’s usual workflow.
Glaze comes after that, applied over the top of any underglaze decoration once it’s dry, and then fired to its own final temperature. That order matters because it’s what allows the transparent or semi-transparent glaze layer to sit protectively over the underglaze artwork without disturbing or smudging it during application.
Some underglaze products are also formulated to be used at the bisque stage without any additional clear glaze on top, though for functional ware that will hold food or liquid, a clear glaze layer over the underglaze decoration is still the standard, safer approach most studios recommend.
Can You Use One Without The Other
Glaze can absolutely be used on its own, without any underglaze at all, and plenty of pieces are finished this way, especially simple solid-colour functional ware where painted decoration isn’t part of the design. In that case, the glaze itself provides both the colour and the protective finish.
Underglaze without a final glaze is more of a mixed bag. It’s technically possible for purely decorative pieces that won’t hold food or liquid, since underglaze on its own doesn’t form the same waterproof, food-safe barrier a proper glaze layer does. For anything functional though, most studios strongly recommend a clear or coloured glaze over underglaze decoration, both for durability and for genuine food safety.
In practice, most decorated functional pottery genuinely uses both together, underglaze for the detailed colour work and pattern, glaze over the top to protect it and give the piece its final food-safe, wipeable surface.
A clear glaze is a particularly popular choice over underglaze decoration specifically because it protects the artwork without hiding it, letting the painted detail show through while still providing the same waterproof, food-safe barrier a coloured glaze would give a plain piece.
What Competing Guides Leave Out
A lot of beginner guides explain the theory clearly enough but skip over how easy it actually is to mix the two products up on a shared studio shelf, especially early on. In our experience at Le Studio Art Space’s Ceramic Studio, new members occasionally reach for the wrong jar simply because both come in small, similarly labelled containers, and the practical fix is just learning to check texture and consistency, underglaze tends to feel more like paint, while glaze often feels slightly thicker or more slip-like.
Packaging and labelling habits vary between manufacturers too, which most guides don’t mention. Some underglaze lines use bold, obviously paint-like branding, while others package it almost identically to their own glaze range, so it’s genuinely worth double-checking the label rather than assuming by appearance alone, particularly with an unfamiliar brand.
Another gap is what happens if you apply them in the wrong order by mistake. Glazing before underglaze generally won’t work the way you’d want, since the underglaze detail would sit on top of an already-fired glass surface instead of being sealed protectively beneath it, so getting the sequence right genuinely matters for the final result.
A Simple Way To Remember The Difference
A genuinely useful mental shortcut is to think of underglaze as the paint and glaze as the varnish. Underglaze adds the colour, detail, and artwork, much like paint on a canvas, while glaze goes over the top afterward, protecting that artwork and giving the whole piece its final, food-safe, glass-like finish.
Another way to remember the order is simply the name itself. Underglaze literally goes under the glaze, applied earlier in the process, while glaze itself is always the last layer before the final firing, sitting protectively on top of everything underneath it.
Once that basic order clicks, the rest of the confusion around glaze vs underglaze tends to sort itself out fairly naturally, since most other questions about the two products really just come back to that same simple sequence.
The easiest way to get comfortable with glaze and underglaze is to work with both hands-on. Join a decorating session at Le Studio Art Space in Mordialloc and try it yourself.
Frequently Asked Questions
Can I use underglaze as a substitute if I’ve run out of glaze?
Not really, they do different jobs. Underglaze doesn’t form the waterproof, food-safe glass layer that glaze does, so it isn’t a safe substitute for functional ware that needs a proper glaze finish.
Is it obvious which jar is glaze and which is underglaze on a shelf?
Not always, packaging varies a lot between manufacturers. In our experience, checking the consistency, underglaze tends to feel more like paint, and reading the label carefully is more reliable than judging by the container alone.
Do I always need to put glaze over underglaze decoration?
For anything functional that will hold food or liquid, yes, a clear or coloured glaze over the top is the safer, standard approach. Purely decorative pieces have a bit more flexibility, but most studios still recommend it.
What happens if I accidentally glaze before applying underglaze?
The underglaze detail would sit on top of the fired glaze rather than being sealed protectively beneath it, which generally doesn’t give the result you’re after. Getting the order right, underglaze first, matters for the final look.
Is underglaze harder to apply well than glaze?
Not necessarily harder, just different. Underglaze behaves more like paint and rewards a steady hand for fine detail, while glaze is more about even coverage and correct thickness across the whole piece.
This article is provided for general educational purposes by Le Studio Art Space and reflects publicly available product information and common studio practice.