Cobalt Carbonate Dosage Calculator

Enter your glaze batch weight, target cobalt oxide percentage, and carbonate purity to calculate the exact cobalt carbonate dose needed for consistent glaze coloring.

Created by Luis GonzalezLast updated: May 9, 2026

How to Use This Calculator

1
Enter Dry Glaze Batch Weight
Input the total dry weight of your glaze batch in grams. This is typically the weight of all powdered ingredients.
2
Specify Target CoO %
Enter the desired cobalt oxide percentage in your final fired glaze (e.g., 0.5% for a medium blue). Typical range is 0.25–2%.
3
Input Cobalt Carbonate Purity
Provide the cobalt content purity of your cobalt carbonate powder as a percentage. Standard reagent grade is around 71%.
4
Enter Glaze Water Content
If your glaze batch includes water, enter its percentage. Enter 0 for a dry batch, as the calculation is based on dry weight.
5
Review Your Results
The calculator will display the exact grams of cobalt carbonate needed, its percentage of the glaze batch, and the equivalent cobalt oxide.

Example Calculation

A ceramic artist wants to achieve a medium blue hue in a 1,000-gram dry glaze batch, targeting 0.5% CoO, using cobalt carbonate with 71% purity.

Dry Glaze Batch Weight (g)

1,000

Target CoO % (%)

0.5

Cobalt Carbonate Purity (%)

Glaze Water Content (%)

Results

11.18 g

Tips

Weigh Accurately

Use a precise digital scale (to 0.01 g) for measuring cobalt carbonate. Small variations in dosage can lead to noticeable differences in the final fired color intensity.

Test Fire Small Batches

Always perform small test firings with new glaze formulations or dosage adjustments. Factors like kiln atmosphere, firing temperature, and other glaze components can alter the final cobalt blue hue.

Beware of Overdosing

Cobalt is a potent colorant. Too high a percentage (e.g., above 1.5-2% CoO) can lead to an overly dark, almost black color, or cause glaze defects like crawling or pinholing due to its fluxing properties.

Precision Glaze Coloring with the Cobalt Carbonate Dosage Calculator

The Cobalt Carbonate Dosage Calculator provides ceramic artists and chemists with the exact grams of cobalt carbonate needed for any glaze batch, based on target CoO%, batch weight, and purity. This tool ensures consistent color intensity, from pale blue tints to deep cobalt blues, and helps avoid glaze defects from incorrect dosages. Understanding the chemical transformation of cobalt carbonate into cobaltous oxide (CoO) during firing is key to achieving desired ceramic results.

Chemical Considerations in Ceramic Glaze Formulation

Cobalt carbonate is a cornerstone colorant in ceramic glazes, prized for its ability to produce vibrant blue hues. Its effectiveness stems from its transformation into cobaltous oxide (CoO) during firing, which then integrates into the glaze matrix. The target CoO% in a glaze is a critical parameter: concentrations as low as 0.25% can yield a pale blue tint, while 0.5-0.75% typically results in a medium blue. However, exceeding 1.5% CoO can lead to an intense, almost black blue, and may also cause glaze defects such as pinholing or crawling due to cobalt's fluxing properties. Accurate weighing in grams and thorough mixing are essential for achieving consistent and predictable results in the kiln.

Calculating Cobalt Carbonate for Glazes

Calculating the correct dosage of cobalt carbonate for a glaze involves several steps, accounting for the target cobalt oxide percentage, the dry weight of the glaze, and the purity of the cobalt carbonate powder.

Dry Glaze Weight (g) = Glaze Batch Weight (g) × (1 - Water Content (%)/100)
Cobalt Oxide Needed (g) = (Target CoO (%)/100) × Dry Glaze Weight (g)
Cobalt Carbonate Raw (g) = Cobalt Oxide Needed (g) × (CoCO₃ MW / CoO MW)  // MW Ratio ~1.587
Cobalt Carbonate Needed (g) = Cobalt Carbonate Raw (g) / (Cobalt Carbonate Purity (%)/100)

Here, Glaze Batch Weight is the total weight, Water Content adjusts to dry weight, and Target CoO is the desired percentage. The molecular weight ratio (CoCO₃ MW=118.94, CoO MW=74.93) is crucial for converting between the oxide and carbonate forms.

💡 Just as precise measurement is crucial for glaze chemistry, our Reconstitution Volume Calculator highlights the importance of accurate liquid and powder mixing in other chemical preparations.

Dosing Cobalt Carbonate for a Medium Blue Glaze

A ceramic artist is preparing a 1,000-gram dry glaze batch and wants to achieve a medium blue by targeting 0.5% CoO. The cobalt carbonate powder has a purity of 71%, and the batch contains no water (0% water content).

Enter Dry Glaze Batch Weight: Input "1,000" g.
Enter Target CoO %: Input "0.5".
Enter Cobalt Carbonate Purity: Input "71".
Enter Glaze Water Content: Input "0".
Calculate Dry Glaze Weight: 1,000 g × (1 - 0/100) = 1,000 g.
Calculate Cobalt Oxide Needed: (0.5 / 100) × 1,000 g = 5 g CoO.
Calculate Raw Cobalt Carbonate: 5 g CoO × 1.587 = 7.935 g.
Calculate Cobalt Carbonate Needed (adjusted for purity): 7.935 g / (71 / 100) = 7.935 / 0.71 = 11.176 g. Rounded, this is 11.18 g.

The artist needs 11.18 grams of 71% pure cobalt carbonate to achieve a 0.5% CoO target in their 1,000-gram dry glaze batch.

💡 When handling powdered chemicals like cobalt carbonate, safety is paramount. Our Spill Volume Calculator, while for liquids, underscores the need for preparedness and proper handling procedures for any chemical substance.

Situations Requiring Glaze Testing Beyond Calculation

While precise calculations provide an excellent starting point for ceramic glaze formulation, there are specific scenarios where relying solely on theoretical dosages can lead to unexpected results, necessitating practical test firings. Factors such as the kiln's firing atmosphere (e.g., reduction versus oxidation), the presence of other fluxing agents or colorants in the glaze (e.g., zinc can mute cobalt blue, titanium can make it greenish), and the specific clay body being used can all significantly alter the final fired color, texture, and surface quality. Therefore, it is strongly recommended to conduct small-batch test firings, creating multiple test tiles (e.g., 3-5 variants with slight dosage adjustments) to validate the calculated results, especially when developing new glazes or working with unfamiliar materials.

Frequently Asked Questions

What is cobalt carbonate used for in ceramics?

Cobalt carbonate is a widely used colorant in ceramics, primarily to produce various shades of blue in glazes, slips, and clay bodies. Upon firing, it transforms into cobalt oxide (CoO), which is responsible for the intense blue hue, ranging from pale sky blue at low concentrations (0.25%) to deep navy or even black at higher percentages (over 2%).

Why is cobalt carbonate purity important?

Cobalt carbonate purity is critical because it directly affects the actual amount of coloring agent (cobalt oxide) introduced into the glaze. A lower purity means more powder is needed to achieve the same target cobalt oxide percentage, impacting both the dosage calculation and the overall consistency of the fired color, making accurate purity data essential for reliable results.

What is CoO and its role in glazes?

CoO, or cobaltous oxide, is the active coloring agent derived from cobalt carbonate during the firing process in a ceramic kiln. It is responsible for the characteristic blue color in glazes. The target percentage of CoO in a glaze is a direct determinant of the final blue's intensity, with higher percentages yielding deeper, more saturated hues.

How does water content affect glaze calculations?

Water content in a glaze batch affects calculations by diluting the dry weight of the glaze, meaning the actual amount of dry material available for the colorant to be mixed with is less than the total wet weight. To ensure accurate percentage-based dosages, it's crucial to calculate the dry glaze weight, excluding water, as the colorant concentration is based on the solid components.