What is Specific Gravity and Why It Matters for Your Glazes

Hey there! It's Ella again, and today we're diving into one of the most important concepts for successful glazing: specific gravity. I know it sounds a bit technical, but once you understand this simple measurement, your glazing results will become far more consistent and predictable.

TLDR: Download our handout here Hydration and Specific Gravity Instructions

What Exactly is Specific Gravity?

Think of specific gravity as your glaze's "thickness fingerprint." Technically, it measures how dense your liquid glaze is compared to water. Water has a specific gravity of 1.0 (100 ml water = 100 grams on a scale), so when your glaze measures 1.45 (100 ml = 145 grams on a scale), it means the glaze is 1.45 times heavier than the same volume of water.

In practical terms, specific gravity helps you know if your glaze will apply evenly, provide proper coverage, and fire the way you expect.

Why Specific Gravity is Your Secret Weapon

Getting your specific gravity right is like having a reliable recipe - it takes the guesswork out of glazing. Here's why it matters so much - 

Consistent Coverage: A glaze that's too thin (low specific gravity) won't give you proper coverage, leading to thin, streaky results. A glaze that's too thick (high specific gravity) and you'll get runs, drips, or an overly heavy application that can cause crawling or other defects.

Predictable Results: When your specific gravity is in the sweet spot, you can dip piece after piece knowing each one will get the same amount of glaze. You no longer have to wonder why some pieces turned out perfect while others looked completely different.

Color Consistency: This is especially important with Five Glaze colorants. The right specific gravity ensures your colors develop as intended - not too light, not too saturated.

Professional Finish: Consistent specific gravity gives you that smooth, even finish that makes your work look professional and intentional.

Testing Your Glaze's Specific Gravity: The 100 Gram Method

Ready to master this technique? Here's the step-by-step process I use for all my Five Glaze testing:

Tools You'll Need:

• 100ml graduated cylinder
• Digital kitchen scale (sensitive to hundredths of a gram for best results)
• Whisk or spatula
• Your mixed liquid glaze

Step-by-Step Testing Process

1. Prepare Your Equipment

• Weigh your empty, clean 100ml graduated cylinder
• Tare your scale with the cylinder on it ( this ensures you’re only measuring the glaze, not the container).

2. Fill and Weigh

• Fill the graduated cylinder with your glaze mixture to exactly the 100ml line
• Make sure there are no air bubbles - tap the cylinder gently if needed
• Weigh the filled cylinder on your tared scale

3. Calculate Your Specific Gravity The math is beautifully simple:

Specific Gravity = Weight of Glaze (in grams) ÷ 100

Let's say your filled cylinder weighs 145g on the tared scale:

• Glaze weight = 145g
• Specific Gravity = 145g ÷ 100 = 1.45

4. Check Against Your Target Range For Five Glaze bases, we recommend a specific gravity between 1.4 - 1.5.

Visually, your glaze should have the consistency of heavy cream - thick enough to coat well, but fluid enough to level out smoothly.

5. Make Adjustments

• Too thick? Specific gravity above 1.5 means you need to add water in small increments.
• Too thin? Specific gravity below 1.4 means you need to let some water evaporate.

Always mix thoroughly and retest after each adjustment.

Pro Tips for Accurate Testing

Start Thick: It's much easier to thin a glaze than to thicken it. When you're first mixing your Five Glaze, err on the thick side and add water gradually.

Temperature Matters: Test at consistent room temperature. Hot glaze liquids will read differently than cool glaze liquids, so let everything come to room temperature before testing.

Mix Well First: Always give your glaze a thorough stir before testing. Settled particles can throw off your reading.

Keep Records: Jot down the specific gravity that works well for you. This creates your own reference library for future mixing.

Troubleshooting Common Issues

Getting inconsistent readings? Make sure you're filling the cylinder to 100ml each time. A few milliliters difference can affect your calculation.

Glaze seems right visually but specific gravity is off? Trust the numbers. Visual consistency can be deceiving, especially as you're learning.

Can't get into the target range? Double-check your mixing ratios first. If those are correct, small variations are normal and workable.

Making Specific Gravity Work for You

Once you've nailed down the right specific gravity for your favorite Five Glaze combinations, you'll find that glazing becomes so much more predictable and enjoyable. No more mystery about whether a piece will turn out well - you'll know before it goes in the kiln.

This measurement might seem like an extra step when you're eager to start glazing, but I promise it's time well invested. Think of it as insurance for your pottery - a few extra minutes of testing can save hours of disappointment later.

Ready to put this into practice? Grab your graduated cylinder and scale, and start building your specific gravity confidence. Your future self (and your pottery) will thank you for developing this essential skill.

Questions about specific gravity testing or getting unexpected results? I'd love to help you troubleshoot - feel free to reach out!