Line Testing Multiple Colorants: Your Fast Track to Custom Colors

Hey everyone! It's Rainy, and today I'm sharing one of my absolute favorite techniques for exploring custom colors with Five Glaze - systematic line testing. This method lets you test multiple colorants and percentages efficiently, building your personal color library fast while keeping costs down.

Line testing is like speed dating for glazes - you can explore lots of options quickly and find the perfect matches for your pottery style!

Why Line Testing is a Game-Changer

Traditional testing can take forever - mixing one color at a time, firing individual tests, waiting for results. Line testing flips that on its head by letting you:

Test Multiple Variables at Once: Compare different colorants side by side in the same firing.

Build Your Library Fast: One firing session can give you data on dozens of color combinations.

Save Money: Testing in small 100 grams batches means you're not committing expensive colorants to large batches.

Make Better Decisions: See how colorants behave across different percentages simultaneously.

Reduce Kiln Time: Pack more information into each firing.

Supply List for Efficient Line Testing

Having everything organized upfront makes the whole process smoother and more enjoyable:

Essential Supplies:

• Digital scale (accurate to 0.1 grams)
• Containers with lids (deli containers are perfect!)
• Permanent markers for labeling
• Masking tape
• Small measuring spoons
• Small whisk or stirring tools
• Five Glaze base bag (e.g., Serotonin)
• Selection of colorants you want to test (e.g., Mason Stain)

Organization Supplies:

• Test tiles (uniform size and clay body)
• Notebook or spreadsheet for recording
• Small brushes for application
• Camera for documenting results
• 100 ml graduated cylinder for water measurement

Pro Tip: Deli containers are ideal for 100 grams batches—they stack well, seal tightly, and are inexpensive.

Understanding Glaze Recipe Basics

Here’s a key concept:

• Base glaze = the glaze recipe without any colorants (e.g., Serotonin).
  

• Full formula glaze = base glaze plus colorant(s).

Colorants are just pigments—they aren’t glazes by themselves.

When talking about colorant percentages, we mean a percentage of the base glaze weight, not the total mix. Your base glaze is always 100%, and the colorant percentage is added on top. That’s why your total formula is more than 100% (e.g., 100% Serotonin base + 5% colorant = 105%).

Planning Your Line Test Strategy

Before you start mixing, take a few minutes to plan your approach. This will save time and ensure your results are useful.

Choose Your Variables:

• Colorant Types: Pick 3-5 colorants you want to explore.
• Percentage Range: Standardize the increments (e.g., 3%, 5%, 7%, 9%).
• Application Method: Choose dipping, brushing, or pouring—and stick to the same method for all tests.

Sample Planning Layout:

Let's say you want to test 4 colorants at 4 different percentages:

• Colorant A: 3%, 5%, 7%, 9%
• Colorant B: 3%, 5%, 7%, 9%
• Colorant C: 3%, 5%, 7%, 9%
• Colorant D: 3%, 5%, 7%, 9%

That's 16 different combinations in one firing!

The Math For Line Testing

Here's the simple math for each 100 grams test batch:

Colorant Weight = (Desired Percentage ÷ 100) × 100 grams

Quick Reference Chart:

• 3% test: 3 grams colorant + 100 grams base
• 5% test: 5 grams colorant + 100 grams base
• 7% test: 7 grams colorant + 100 grams base
• 9% test: 9 grams colorant + 100 grams base

Step-by-Step Line Testing Process

Step 1: Safety First

Wear PPE—NIOSH N95 mask, safety glasses, and gloves. Work in a well-ventilated area.

Step 2: Label Your Containers

Mark each container with:

• Base Glaze Name
• Colorant Name
• Colorant Percentage
• Date
• Your initials

Example: "Serotonin Red Iron Oxide 5% - 8/8/25 - R"

Step 3: Weigh Dry Materials

1. Weigh 100 grams of the base glaze into each container.
2. Weigh out the colorant separately.
3. Add the colorant to base glaze.
4. Double-check your labels!

Step 4: Hydrate Each Batch

1. Add 90 grams of water to each container.
2. Mix thoroughly, let sit, then mix again.
   
3. Adjust glaze thickness so all batches match.

Step 5: Apply to Test Tiles

• Use identical test tiles for fair comparison.
• Apply glaze on each test tile using the same method.
• Label tiles clearly to match your containers.
• Take photos of the unfired tiles for reference.

Step 6: Fire and Evaluate

• Fire all tiles together using your standard mid-range firing schedule.
• Once cooled, lay them out in order and evaluate systematically.

Reading and Recording Your Results

This is where the magic happens! Spend time interpreting your results to build your knowledge base.

What to Look For:

• Color Development: How does the color change across percentages?
• Surface Quality: Compare each test to your base glaze with no colorant.
• Defects: Note any bubbling, pinholing, crawling, or texture changes.
• Saturation Sweet Spot: Find the lowest percentage that gives you the color intensity you want.

Documentation Tips:

Create a simple chart for each colorant (see example below), keep fired tiles organized, and photograph in consistent lighting.

COLORANT A: 

 

Remember: Choose the lowest percentage that gives you the desired effect - colorants are expensive, so being economical saves money!

Advanced Colorant Testing Strategies

Once you're comfortable with basic line testing, try these advanced approaches.

Blended Colorants:

Test combinations with multiple colorants. For example:

• Colorant Mix A: 2% Cobalt + 3% Rutile (5% total)
• Colorant Mix B: 4% Red Iron Oxide + 1% Cobalt (5% total)

Different Base Glazes:

Run the same percentages across different Five Glaze bases to compare interactions.

Firing Variations:

Dip multiple tiles from one batch and label them for different schedules (slow cool, fast fire, different cones). Cooling cycles can dramatically change results.

Troubleshooting Common Issues

• Inconsistent Results Between Tests: Check that you're applying glaze at the same thickness and firing tiles in similar kiln positions.
• Unexpected Color Shifts: Some colorants react to clay body iron or kiln atmosphere.
• Surface Defects at Higher Percentages: This is exactly what line testing is designed to catch. Note where problems start and stay below that percentage threshold.
• Colors Too Similar: Try wider percentage gaps (2%, 6%, 10%) or different colorant families.

Building Your Custom Color Library

Each successful line test becomes a building block in your personal glaze library!

Keep Physical Samples:

Store your best test tiles in organized boxes with labels. These become your go-to reference when planning projects.

Digital Documentation:

• Photograph results in consistent lighting
• Create spreadsheets with recipes and notes
• Note which clay bodies and firing schedules were used

Scale-Up Notes:

When you find winners, calculate the amounts needed for full batches. Our Base Glaze bags are 2,250 grams (5lbs) which makes one gallon of wet glaze. Here is the formula:

Desired Batch Size = (Colorant Percentage ÷ 100) × Desired Batch Size Weight (grams)

For example:

• (5% ÷ 100) × 2,250 grams = 112.5 grams colorant needed
• Use 2,250 grams Base Glaze bag, then add 112.5 grams colorant and 2,040 grams water.

Making Line Testing a Regular Practice

The most successful potters I know make line testing a regular part of their studio practice.

Seasonal Testing: Try new colorants or combinations each season

Project-Specific Tests: Create custom palettes for specific bodies of work

Collaboration Tests: Share costs and results with studio mates

Documentation Reviews: Regularly review your test library for inspiration

Ready to Start Your Line Testing Journey?

Line testing might seem like a lot of work upfront, but it's honestly one of the most valuable investments you can make in your pottery practice. You'll develop an intuitive understanding of how colorants behave, build confidence in your glaze mixing, and create unique colors that become part of your artistic signature.

Start small - pick two colorants you're curious about and test them at 3%, 5%, and 7%. That's just six small batches, but you'll learn so much from that single firing!

The beauty of working with Five Glaze is that you have a reliable, well-tested base glaze to build off of. Our base glazes are formulated to be stable and forgiving, giving you the confidence to experiment knowing you're starting from solid ground.

Ready to dive into systematic line testing? Have questions about organizing your tests or interpreting results? I'd love to help you build your custom color library - reach out anytime!