Choosing the Right Clay

A practical guide from the team at Decopot 

Whether you're just starting out on the wheel or you've been throwing for years, choosing the right clay is one of the most important decisions you'll make. The good news? Once you understand a few key factors, it becomes a lot easier — and maybe even a little fun. 

Here's what we recommend thinking through before you make your choice. 

Understanding the Three Clay Categories 

Before diving into the selection factors, it helps to understand the three main types of kiln-fired clay body: 

Earthenware 

Low-fire clay, typically fired between around 999–1060°C (Cone 06–04). Smooth and easy to work with, with bright glaze colour response. More porous after firing than stoneware and typically requires a durable, well-fitted glaze for food-contact applications. Historically common in schools and introductory pottery programmes due to its low firing temperature and forgiving nature. Generally, the most affordable clay type. 

Stoneware 

Mid- to high-fire clay, typically fired between around 1160–1300°C (roughly Cone 4–10). Stronger and more durable than earthenware, and often vitreous (very low water absorption) when fired to the correct temperature. Stoneware is the most popular choice in New Zealand studios because it combines durability, versatility and a wide firing range. Most stoneware bodies work well for wheel throwing, hand building and functional ware. 

Porcelain 

Mid- to high-fire clay, typically fired between around 1150–1300°C (roughly Cone 3–10). Very fine, white-firing and often translucent when fired. While porcelain can be highly workable and responsive on the wheel, it is generally less forgiving than stoneware because of its high shrinkage lower green strength, and greater tendency to warp or crack during drying and firing. We recommend gaining experience with stoneware before moving to porcelain. 

Note on Cone numbers:  

Cone numbers are a standardised scale (Orton) used worldwide to describe heatwork during firing. The cone equivalents shown above are approximate only. Actual temperatures vary depending on kiln design, firing speed and firing schedule. Always use the clay body's recommended firing range in °C as the primary guide. 

Before You Start: Think About Your Experience Level 

Your experience level should shape which clay you reach for first. 

  • New to pottery: Choose a stoneware with moderate plasticity. A small amount of grog can improve stability, although smooth bodies such as FSZ, Atelier W and PW20 are also excellent beginner choices. Avoid pure porcelain until you've built some confidence — it is less forgiving during throwing, drying and firing. 

  • Intermediate: You can start exploring speckled bodies, darker clays, and clays with specific technical properties like low water absorption for functional ware. 

  • Experienced / professional: The full range is available to you. Experienced potters will generally find it easier to take advantage of porcelains, high-fire grogged bodies and specialist sculptural clays. 

Not sure where to start?

For most beginners, a mid-fire stoneware is the safest and most rewarding choice. Standard Stoneware RW1002 and PRIMO PW20 are our most popular starting clays — both are smooth, plastic (easy to work and shape), forgiving, and well suited to both wheel throwing and hand building. If in doubt, start with one of these.


1. Start with your kiln's firing range

This is the non-negotiable first step. Your kiln's temperature range determines which clays you can fire successfully. Most kilns will display their maximum temperature in °C — always match this to the clay's recommended firing range before purchasing. 

  • Low-fire kilns (approx. 999–1137°C / Cone 06–01): suited to earthenwares and some terracottas. Note that most earthenwares are fired in the lower part of this range, around 999–1060°C. 

  • Mid-fire kilns (approx. 1165–1240°C / roughly Cone 4–7): the most popular range in NZ studios. Most of our stoneware range and PRIMO PW20 fall here. 

  • High-fire kilns (approx. 1263–1305°C / roughly Cone 8–10): for dense, durable stoneware and high-fire porcelains. Required for PRGI-4002 and PRGF4005 (minimum 1240°C). 

Important: Cone numbers are a useful reference point but the temperature in °C from the clay's datasheet is the most reliable guide. Cone temperatures can vary slightly depending on your kiln and firing speed.

Important: Atelier R (Red Stoneware) has a maximum firing temperature of only 1160°C — lower than most other clays in this range. Always check the clay's recommended range before purchasing. 

2. Think about how you'll be working 

  • Wheel throwing: Look for smooth, plastic (easy to shape) bodies. Standard Stoneware RW1002, FSZ, White Stoneware (Atelier W), WFSZ 2002, PRIMO PW20, and Cacao RW1302 are all excellent. Hanjiki Half Porcelain and PRIMO Highfire Porcelain work well for experienced throwers.

  • Hand building: Moderate grog (10–25%) adds strength and helps slabs and coils hold their shape. Toast RW1802, WM2502, W2502, W2505, WMS 2002GG, WMSB, and Cacao RW1302 are all reliable options. PRIMO PW20 is also a good hand-building clay.

  • Large-scale sculpting: High grog is essential. RTM5015 (50% chamotte) is engineered for large sculptural builds with only 3.5% fired shrinkage. PRGF4005 (40% grog) is designed for sculpture, murals and Raku.

  • Throwing and modelling: PRGI-4002 (40% impalpable grog) is a high-fire body suited to both throwing and modelling fine detail — distinct from RTM5015 and PRGF4005 which are not suited to throwing.

  • Slip casting: Use Porcelain Casting Slip V7-3 only — it is not interchangeable with throwing or hand-building clay.

  • Schools and community studios: Standard Stoneware RW1002, White Stoneware (Atelier W), FSZ, Toast RW1802, and PRIMO PW20 are reliable, forgiving choices that deliver consistent results across a wide firing range.

3. Consider the size of your work 

As a general rule, larger hand-built and sculptural work benefits from increased grog content because it reduces shrinkage and improves structural stability. RTM5015's 50% chamotte results in just 3.5% fired shrinkage, compared with 5–7% for many lower-grog bodies. White-firing bodies such as PRIMO PW20 (~16%) and porcelains such as PRIMO Highfire (~19%) exhibit significantly higher shrinkage than most stonewares, which needs to be factored into your planning. 

4. Decide on the texture and finish you want

Grog (also called chamotte) is crushed, pre-fired clay that has been ground and added back into the clay body. It is one of the most important factors in clay selection: 

  • No grog: smooth, refined finish — porcelains, PRIMO PW20, FSZ. The clay feels silky but can feel slippery and collapse more easily, particularly for beginners.

  • Fine grog (0–0.2mm, 10–20%): slight texture with good stability — Standard Stoneware, Toast RW1802, Cacao RW1302, WMS 2002GG, Nigra 2002, WFSZ 2002. A small amount of grog gives the clay 'tooth' — a slight resistance that helps it hold its shape. Many beginner-friendly clays sit in this range.

  • Moderate grog (0–0.5mm, 20–25%): more texture and strength — W2505, WMS 2005B, WMS 2005GG, R2505, PRGF4005. Good for hand building and larger forms.

  • High grog (50%, 0–1.5mm): coarse texture and maximum strength — RTM5015. Not suited to wheel throwing.

For speckle effects: WMS 2002GG, WMS 2005GG, WMSB, WMS 2005B, and WMS 2502 all develop their characteristic spots from 1150°C. Fire below this temperature and the surface will appear plain.

5. Choose your fired colour

  • Whites and creams: Standard Stoneware RW1002, FSZ, White Stoneware (Atelier W), W2502, W2505, WM2502, WFSZ 2002, WMS 2502, PRIMO PW20, Hanjiki
    Half Porcelain, PRIMO Highfire Porcelain.

  • Warm earthy and brown tones: Cacao RW1302 (walnut–chocolate brown), Toast RW1802 (terracotta–red brown), WMSB (apricot–yellow–khaki), R-Terracotta (light red–red brown), PRGI-4002 (light toasted brown), PRGF4005 (light tan brown).

  • Speckled / spotted: WMS 2002GG and WMS 2005GG (rose–grey spots), WMSB and WMS 2005B (apricot–khaki spots), WMS 2502 (cream with spots).

  • Dark / dramatic: Nigra 2002 (black), Cacao RW1302 (deep chocolate brown at 1220°C).

  • Red tones: Atelier R (red, max 1160°C), Red Stoneware with Grog R2505 (red).

Always run a test firing — especially for speckle clays and Cacao, where the full colour develops at higher temperatures.

6. Think about functional requirements

For durable functional ware, fired water absorption is one of the most important figures to consider. Lower absorption generally indicates a denser, more vitreous clay body. However, food safety and long-term durability also depend on appropriate glaze selection, glaze fit, glaze durability, and correct firing.

As a general guide:

  • WFSZ 2002: 0.1% at 1200°C — exceptionally low absorption.
  • Cacao RW1302: reported 0.0% at 1220°C — effectively vitreous.
  • PRIMO Highfire Porcelain: 0.1% at 1260°C — exceptionally low absorption.
  • Toast RW1802: 0.4% at 1240°C — very low absorption at the upper end of its range.
  • PRIMO PW20: 2% at 1200°C — suitable for functional ware.
  • Nigra 2002: 2.5% at 1200°C — suitable for functional ware when properly glazed.
  • Standard Stoneware RW1002: 1.8% at 1240°C — suitable for functional work at higher temperatures.
  • Atelier R (Red Stoneware): 4.5% at 1100°C — glaze thoroughly for food-contact use.
  • RTM5015 and PRGF4005: 6–7.4% absorption — primarily intended for sculptural rather than unglazed functional applications. 

7. Check your glaze compatibility 

The coefficient of thermal expansion (CTE) varies between clay bodies — mismatched CTE between clay and glaze can cause crazing or shivering. Full CTE data is available in the individual Sibelco technical datasheets. PRIMO PW20 generally contributes to well-fitting glazes and works especially well with Abbots Clear between 1160°C and 1200°C. Cacao RW1302 works particularly well with iron, copper, and reactive and variegated glazes. Always test a new clay/glaze combination before a full production run. 

8. Consider cost 

Clay price varies across the range. As a general guide: 

  • Earthenwares are generally the east expensive clay bodies. Within the Primo Pro range, most studio stonewares represent the best value for everyday pottery work 

  • Porcelains are generally more expensive, reflecting the finer raw materials and more demanding production process.

  • Sculptural and high-grog bodies (RTM5015, PRGI-4002, PRGF4005) are priced to reflect their specialist formulations and larger bag sizes.

Check current pricing on our website. Orders of 20 or more bags attract a 15% discount across most of the range.

9. Test before you commit

Even when you've done everything right on paper, there's no substitute for a small test run. Fire a few pieces, try your glazes, and check the results before scaling up. Pottery rewards patience — and a little testing upfront saves a lot of frustration later.