Techno File: The Cost of Glaze Joe Thompson

Appears in the April 2023 issue of Ceramics Monthly.

Understanding the factors that determine materials costs and charting their prices can help you find out which of your glazes are more expensive and occasionally when testing substitutions could be beneficial.

Defining the Terms 

Frit: Frits are commercially made, powdered glaze ingredients with a specifically defined chemistry. Frit manufacturers take raw glaze ingredients, melt them to form a glass, then cool and grind the glass to form a powder. This powder can be added to a glaze, providing a consistent chemical composition not found in natural minerals. Frits can be made for a variety of commercial purposes but the frits commonly used in glaze recipes are typically there as a convenient source of boron. Boron is an effective way to lower the melting temperature of a glaze without radically changing other characteristics, but most natural boron sources have issues when used in glazes (such as solubility).

Metal Oxides: In ceramics, metal oxides impart color to glazes, clay bodies, slips, and engobes; however, not all are colorants. Most common glazes used in ceramics are a composite of a base transparent glaze with an added metal oxide to color it. Common metal oxides are iron oxide, cobalt oxide, chrome oxide, copper oxide, manganese dioxide, and nickel oxide. Some of these have carbonate forms (e.g. cobalt, copper, nickel). Some are stable and predictable in their color contributions (e.g. cobalt, chrome). 

Specific Gravity: The weight of a glaze slurry compared to water. Different glazes optimize to different specific gravities, but 1.4 to 1.5 is typical. Each glaze is different and each person will have different preferences as to how thick they like a glaze.

What are Glazes?

Glazes are thin surface coatings; in ceramics they’re a special glass that optimally provides a durable and waterproof layer over the clay. In their unfired state, they’re made of a specific combination of powdered rocks, minerals, frits (man-made powders with specific chemistry), and metal oxides.

I won’t attempt to go into what all the powdered ingredients do and why here, but there are multiple categories that do broadly the same thing and are somewhat interchangeable. 

Even though in some cases the specific materials make little difference to the end result, the price of glaze materials is only related to the difficulty of getting them to you in a usable form, so there can be huge price differences within categories.

Factors That Go Into Material Costs

Demand: There are some ingredients (like cobalt and lithium) that get used in glazes but are also in high demand by other industries. There is a good incentive to find and extract deposits, but the price will be set by the market.

Scarcity: Some ingredients are abundant and readily available. Many are only found in a handful of locations. This can dramatically affect the price.

Processing: Some ingredients are found in the format they’re needed, while others need to be processed and refined to remove impurities.

Shipping: This is a huge part of the cost, often more than the material value itself. Glaze materials are heavy and bulky, so even if the ingredient was offered to you for free, if you’re shipping it on a long and complicated journey, then the price will be high regardless. This means that ingredients can be cheap in the country where they’re sourced and prohibitively expensive in another (e.g. Grolleg is cheap in the UK and pricey in the US).

Supplier: Different suppliers will price ingredients differently for a wide range of reasons (source quality, their economy of scale, their packaging costs, factoring shipping costs in, etc.).

Quantity: There is usually a significant price difference between ordering a small amount (as low as 25g for some stains) and ordering a whole 50 lb (25kg) bag. You’ll pay a lot more per pound or kilo if you buy less at once, but that doesn’t mean it’s not a sensible idea.

How Do Glaze Recipes Work?

Typically, glaze recipes are organized in two parts. There are the ingredients needed for a base glaze that add up to 100%, then there are additional ingredients (typically colorants) added that take the total over 100%. 

When mixing up a glaze, you multiply the percentage of that material needed for the glaze by the total amount of base glaze you want. If a recipe calls for 30% silica and you want to mix up a kilogram-sized glaze batch, you’d need 300g of silica (30% of 1000g).

It’s a slightly simplistic view of glaze chemistry (the colorants will affect the behavior as well as the color, so keeping a consistent base and changing colorants will still result in each glaze behaving differently), but very useful from a neatness point of view. The base ingredients tend to be added in the 5–50% range, where colorants are in the 0.1–10% range. Keeping them separate allows for very nicely rounded base recipes. Sometimes you will see the colorants included in the base, and this is chemically more sensible.

The total adding up to more than 100% means that it’s harder to just compare total prices, as in some cases you’ll have significantly more material per kilo of base mix. I added the functionality in a spreadsheet (view my glaze cost calculation spreadsheet by scanning the QR code on the next page) to compensate for this and compare like to like.

Prices

I added my prices to the spreadsheet. You’ll need to change that to your local prices (if you’re not in the UK), as they’ll vary significantly.

But using my prices as an example, you can see at the low end I can get whiting for around $1.19 (£1)/kg (at the moment, but undoubtedly going up) and the most expensive is cobalt carbonate at $203 (£170)/kg. That gives a sense as to how much some ingredients can change in price relative to others.

Looking at just the base ingredients, it’s between $1.19–2.40 (£1–2)/kg for everything other than the frit, which is at $19 (£16)/kg. Frits are a very useful way to get a glaze to melt at cone 6, but they’re typically far more expensive than any other ingredient (higher processing costs, and the Ferro Frits are imported from the US).

Glazes that use a lot of frit will be more expensive than those that don’t. Cone-10 recipes will be much cheaper for this reason, as they don’t need the added boron to melt at the higher temperatures, but the higher temperatures require more energy to reach.

There isn’t usually much you can do about the price of a recipe. Sometimes you can change ingredient selection to keep costs down, but most changes will affect glaze behavior and might not give the same result you started with. For example, reducing boron levels will make a glaze much cheaper but won’t give the same melt and flowing qualities (like in floating blue glazes).

The main thing is to be aware that there is a huge range of material costs and that some things will affect the price far more than others. If you want to keep costs down, you’ll want to avoid recipes with high amounts of cobalt or tin. It might rule certain colors or effects out, but there are plenty of other (cheaper) options!

Converting To Volume

These are prices per kilo of glaze mix, but if you’re using premade glazes, you might be more used to seeing the price per milliliter. There is no direct equivalent as it will depend how much water you add. But a general rule of thumb would be to assume a specific gravity of around 1.45 with around 90–100% added water (so 900–1000g water added per 1000g of glaze powder). This means a kilo of glaze mix will produce around 1.4 liters of glaze (2kg (glaze + water)⁄1.45 = 1.38), and the prices will be around 3/4 per liter as per kilo (so £10⁄kilo equates to around £7.50⁄liter).

Interested in calculating your own glaze costs? View my glaze cost calculation spreadsheet. 

the author Joe Thompson is a graphic designer turned self-taught potter, working out of a small studio in Surrey, UK. He makes functional ceramic work with a focus on the glazing, and creates blog posts and infographics about ceramics. You can find these on his website at www.oldforgecreations.co.uk and on Instagram at @oldforgecreations.