Crystalline glaze pottery is one of the few cases where the firing matters as much as the recipe. The glaze grows visible crystals, often shaped like fans, flowers or snowflakes, as the kiln holds at a set temperature on the way down. For a hobby potter with a programmable electric kiln, they are a realistic but demanding project: the glaze is runny, every pot needs a catcher, and you will lose some work while you learn.
This page is research-based. We compared published crystalline guides from the Glazy wiki, Ceramic Arts Network and Digitalfire, and we did not fire crystalline glazes ourselves. Where those sources give different numbers, we show both.
What makes a crystalline glaze different
The crystals in a true crystalline glaze are zinc silicate, which Digitalfire identifies as the mineral willemite (Zn2SiO4). Zinc oxide and silica in the glaze combine and grow outward from a seed point while the kiln holds in a growth range, so the crystal size depends on time and temperature.
Three things set these glazes apart from ordinary stoneware glazes:
- Very little alumina. Alumina stiffens a glaze melt and blocks crystal growth, so crystalline recipes keep it very low. That is also why they run.
- A lot of zinc and flux. Published base recipes are roughly half frit and a quarter each zinc oxide and silica.
- Little or no clay. Without clay, the glaze settles hard in the bucket and is fragile once dry, so suspenders such as CMC gum or a small amount of bentonite are added.
The result is a background of glossy glass with crystals that look like they float in it. Digitalfire also notes that crystalline glazes almost always craze because they are so high in flux.
Crystal glaze pottery vs crystalline glaze
"Crystal glaze" is used for two different things, which confuses shoppers:
- Crystalline glazes grow their crystals in the kiln, as described on this page. They need a special firing schedule.
- Crystal or "crystal-containing" glazes in jars have small pieces of colored glass frit mixed into the glaze. The pieces melt into bursts of color during a normal firing. Mayco Jungle Gems is a well-known example, fired to cone 06 according to a Mayco dealer listing; see our Mayco Jungle Gems review.
If you want spotty, speckled color with no change to your firing, the jar type is the easy route. If you want true zinc crystals, read on.
The base recipe, in outline
Crystalline glaze recipes are short. The Glazy wiki's starter base is:
| Material | Amount (Glazy starter base) | Job |
|---|---|---|
| Frit 3110 (Ferro) or Frit 75 (Fusion) | 51% | Main flux and glass |
| Calcined zinc oxide | 25% | Forms the crystals with silica |
| Silica, 325 mesh | 24% | Glass former and crystal ingredient |
| Titanium dioxide (addition) | 6% | Encourages crystal seeding |
| CMC gum (addition) | 1 to 2% | Keeps the glaze in suspension and on the pot |
Ceramic Arts Network describes the same proportions: about 25 parts zinc oxide, 25 parts silica and about 50 parts frit or fluxes, with calcined zinc and fine silica. Color comes from small additions: the Glazy guide lists cobalt at 1 to 3%, iron 1 to 5%, copper 1 to 6% and nickel 1 to 3% as starting ranges, not limits. Our frit guide explains what the frit does, and the glaze materials guide covers the colorants.
Zinc oxide, silica and colorants are dry powders. Read each supplier's SDS, weigh and mix them while wearing a fitted NIOSH-approved respirator and gloves, and clean up wet with a sponge or HEPA vacuum, never by dry sweeping.
The firing schedule: melt, crash cool, hold
A crystalline firing has three stages: a full melt, a fast drop (the crash cool), and one or more long holds where crystals grow. Here is the schedule the Glazy wiki publishes for a cone 9 to 10 electric firing:
| Segment | Rate | Temperature | Hold |
|---|---|---|---|
| 1 | Slow preheat | 100°F (38°C) | 30 to 60 min |
| 2 | 325°F (163°C) per hour | 2,200°F (1,204°C) | None |
| 3 | 108°F (60°C) per hour | 2,348°F (1,287°C) | Until cone 10 bends |
| 4 | As fast as the kiln cools | 1,985°F (1,085°C) | 2 hours |
| 5 | Cool | 1,925°F (1,052°C) | 2 hours |
| 6 | Heat | 1,985°F (1,085°C) | 2 hours |
| 7 | Kiln off | Natural cooling | None |
Sources differ on the growth range. Ceramic Arts Network gives about 2,100 to 1,900°F (1,149 to 1,038°C) with a single 3 to 5 hour hold; Digitalfire gives roughly 1,900 to 2,000°F (1,038 to 1,093°C); the Glazy schedule above cycles between 1,985 and 1,925°F. Start with one published schedule, change one thing at a time and keep notes.
Why the crash cool
At peak temperature, the glaze is fully melted and most stray crystal seeds dissolve. Dropping fast to the growth range skips the temperatures where lots of tiny crystals would start at once, so fewer, larger crystals grow instead. Ceramic Arts Network describes taking the kiln well past the glaze's melting point for this reason.
Why the hold
Crystals only grow while the kiln sits in the growth range. Digitalfire notes that holds higher in the range tend to give fewer, larger, more spread-out crystals, and lower holds give smaller, tighter ones. Cycling up and down between two temperatures, as in the Glazy schedule, can create ring patterns in the crystals. After the last hold, the kiln cools naturally.
Can your home kiln do it?
You need three things from an electric kiln:
- A kiln rated for the peak. Most published crystalline schedules peak around cone 9 to 10, so the kiln must be rated to at least cone 10 by its maker. Firing at or near a kiln's maximum wears elements faster; see our kiln elements guide.
- A multi-segment controller. You need ramp-hold programming with several segments, not only a cone-fire preset. Our kiln controller guide explains ramp-hold mode.
- Healthy relays and witness cones. Digitalfire notes that long holds switch the relays far more often than normal firings. Check the peak with a witness cone, as the Glazy author recommends, rather than relying on the controller alone.
Use your kiln at the volts, amps and breaker size its maker lists, and have a licensed electrician check or install the circuit. Keep the clearance and venting your kiln manual specifies, because a long crystalline firing heats the room for many hours.
Catch basins and pedestals
Crystalline glazes run off pots. Every piece needs a catcher, or the glaze will glue it to your shelf. Ceramic Arts Network and Digitalfire describe the same basic setup:
- Make a pedestal. Throw or form a short ring or disk whose top matches the foot of the pot, from the same clay or a refractory mix.
- Make a catch basin. A shallow bisqued dish or saucer sits under the pedestal to collect the glaze that runs.
- Join pot and pedestal. Attach the pot to the pedestal before glazing with a thick paste, such as kaolin and alumina (Ceramic Arts Network) or calcined alumina or kiln wash paste with CMC gum (Digitalfire), so they separate after firing.
- Go thinner near the foot. The glaze flows down during the melt and hold, so a thinner coat on the lower part of the pot leaves less to run off.
- Protect the shelf anyway. Kiln-wash the shelf and leave room so a basin that overflows does not reach the next pot. Our kiln wash guide covers shelf protection.
After firing, tap the pedestal away from the pot along the paste joint. Then grind the sharp glass edge on the foot flat and smooth.
Fired glaze breaks into razor-sharp glass. Wear safety goggles when separating pots from pedestals, as Ceramic Arts Network advises, plus sturdy gloves. Grind feet wet if you can, and wear a respirator when grinding dry, because ground glass and clay dust contain silica.
Common problems
- No crystals. The hold was too short, too hot or too cool, or the glaze was too thin. Check witness cones and the hold temperatures first.
- Hundreds of tiny crystals. Too many seeds survived, or the hold was low in the range. A higher peak, a faster crash cool or a higher hold can help.
- Glaze ran off the pot. Applied too thick at the bottom, or the peak was too hot. Thin the lower half.
- Bare, dry patches. The glaze cracked and fell away before firing because it has little clay. Add CMC gum as published recipes do.
- Crazing. Expected with most crystalline glazes. Digitalfire describes matching the clay body to reduce it.
Are crystalline pots food safe?
Treat crystalline glazes as decorative unless lab testing on your own fired pots says otherwise. Digitalfire explains that they are saturated with flux and low in alumina, so they may leach and are softer than ordinary glazes, and they usually craze. We never promise a glaze is food safe on your pots. For mugs and bowls, many potters keep crystalline glaze on the outside and use a tested liner glaze inside. See our food safe glaze guide.
What you need
A crystalline setup needs a cone 10 rated electric kiln with a multi-segment controller, witness cones, kiln-washed shelves, bisqued pedestals and catch dishes, the dry materials with their SDS sheets, a respirator, a scale and a grinder for feet. If your current kiln cannot reach cone 10 or hold a complex program, our best electric kilns guide compares models by maximum cone and controller.
Sources: Glazy wiki "Getting Started with Crystalline Glazes" (base recipe, colorant ranges, cone 10 schedule, witness cone advice); Ceramic Arts Network, "The New World of Crystalline Glazes" (proportions, growth range and hold, pedestal and catch dish method, separation safety); Digitalfire glossary entry on crystalline glazes (willemite, low alumina, growth zone, catchers, crazing, relays, food-use caution); Mayco dealer listing for Jungle Gems (frit crystals, cone 06) for the crystal-in-jar comparison. Specs checked October 2026.