The Development of Pewabic's Iridescent Glazes

August 05, 2022 5 Comments

A small iridescent, purple vase with an oil-slick appearance on a plain backdrop.


Historic Iridescent vase from Pewabic's archival collection

Pewabic’s signature Iridescent glazes continue to be recognized as the pottery’s most notable achievement over a century after their inception. The current Iridescent glaze roster includes: Blush, Matte Green, and Copper. Blue and Aurora Iridescent glazes are reserved for architectural tile projects.

Co-Founder Mary Chase Perry Stratton’s interest in glaze formulation was inspired in part by American industrialist and friend Charles Lang Freer. Freer championed and collected Mary’s work, challenging her to replicate the luster of vessels brought back from his travels to Persia and China. 

Sepia-toned portrait of American Industrialist, Charles Lang Freer. He is wearing a light suit, his hands are casually folded in front of him, and he has a relaxed smile on his face.



Portrait of Charles Lang Freer, 1919 from The National Portrait Gallery, Smithsonian Institution

After six years of experimentation with metal oxides and atmospheric firings, Pewabic’s first official Iridescent glazes were born.

Mary recounts the forty-two trials of a single glaze option it took to leave an impression on notable Finnish-American architect and designer Eero Saarinen in a letter to her friend Ella Peters in 1940.

“The degree of experiment can be realized from the fact that the glaze that pleased Mr. Saarinen was my forty-second trial in that particular color.”



Historic photo of Pewabic's Co-Founder, Mary Chase Perry Stratton, placing ceramic objects in a small kiln while kneeling.

Photo of Mary Chase Perry Stratton and the Revelation Kiln late 1800s - early 1900s

The hard work paid off as Mary continued to develop her craft after learning from the masters. She writes, “... it is from the experts in these fields that I have received the greatest friendship and encouragement which, of course, is one of the most satisfactory experiences of my life.” Pewabic was not the only pottery producing vibrantly mirrored pots in the Western world–– Mary notes, “My glazes are based on well known formulas which are well within the reach of anyone. These are modified from experiment till I have made them my own.”  

Black and white portrait of Pewabic Co-Founder Mary Chase Perry Stratton mixing glaze elements at the pottery.


Portrait of Mary Chase mixing glaze elements circa 1940

Mary’s trailblazing spirit earned her honorary degrees from the University of Michigan and Wayne State University, “...mainly from the qualities beyond the usual in the various uses of my Iridescent glazes.” Her approach to Iridescent glaze formulation cemented Pewabic as a major force in the ceramic world during that time. 

The means of production have morphed over time as new information regarding the impact on health and safety come to light. For a pottery over a century old, many of the ingredients used during Mary’s exciting first experiments are prohibited from use today. These original ingredients included lead, and in some instances, uranium.


Pewabic glaze sample test circa 1930 with orange, uranium-glazed centers

A majority of the ceramic processes have remained consistent to the early days of Pewabic, but our glaze developers were tasked with getting creative in order to maintain that signature lustrous surface on modern vessels. Continuing Mary Chase’s legacy, we safely produce a curated selection of Iridescent glazes. Our “standard” glazed pieces go through two firings–– an initial bisque firing followed by another after glaze application. Iridescent pots require a third firing and process referred to as “fuming”, where vegetable oil is injected into the kiln, causing a metallic-like flash on the surface of the vessel. 


Pewabic artist hand-painting a large custom piece for a client. The artist is in a studio surrounded by vessels and tiles waiting to be glazed.

Present-day Glaze Development Specialist Alex hand-painting a custom piece

While the formulation of these glazes has changed over time, the high variation between pieces in the same glaze family is consistent with early notes from Mary Chase. In 1940 she wrote that the results were “...always uncertain but less so each time”. This still rings true to this day, as you can see in the variation of outcomes demonstrated in the photo below. 

 Two copper colored iridescent vases side by side against a dark gray/blue background. The vase on the left looks like a vibrant sunset, while the vase on the right has flashes of muted blue on the surface of a mostly copper base. Medium Classic Vases in our Copper Iridescent glaze with two very different results 

A tile depiction of the prophet Malachi surrounded by multi-colored iridescent glazed accent tiles.
Tile depiction of the prophet Malachi surrounded by Iridescent accent tiles at the Basilica of the National Shrine of the Immaculate Conception in Washington, DC.
Various tile installations that prominently incorporate early-Iridescent features can be found in many churches including The Basilica of the National Shrine of the Immaculate Conception in Washington, D.C.–– the largest Catholic Church in North America and one of the ten largest in the world. The many installations in the Basilica's Crypt Church took over six years to complete. 
The era during which Pewabic was commissioned for large-scale architectural projects in holy places is referred to as the "sacred architecture" period.
 A historic Pewabic residential fireplace
To this day our design team and clients work together to incorporate Pewabic's iconic Iridescent glazes into contemporary custom designs. Many of the same accent motifs are still used in current installations and are reserved for architectural production. The glaze selections have changed over time with good reason. Our aim is to continue developing glazes and designs that take inspiration from our history while encouraging the ingenuity of our multi-talented team. 
Blue and green iridescent fireplace set in a bedroom with distressed-wood dressers on either side. There are two round oculus windows above each dresser.

Recent Iridescent bedroom fireplace from our Design Portfolio  

Mary Chase was no stranger to trial and error, and we embrace glaze experimentation with the same curiosity. The inconsistencies that express themselves on the surface perfectly capture the spirit of an organization that does not shy away from appearing handmade. It is that exact human element that ties us indelibly to our craft. 

Various copper iridescent vases lined up against a dark blue backdrop. The vases are shown in a range of sizes. Some of them are holding pale pink and peach colored flowers.

Various Copper Iridescent vases from our collection–– "Petite" vases can only be purchased in-store or during special online releases 

We strive to create one-of-a-kind vessels and tiles to serve as heirlooms or help recount cherished memories for years to come. Mary had a creed that aligns with our mission today. It was that: “The object (has) to be handmade, made from the heart, and designed as a whole in proportion, shape, texture and use.” Our hope is that the work and the creative efforts of our vessel makers, designers, and glaze developers help keep the tangible art of handcraft alive.

5 Responses


March 03, 2023

Nice article. I actual have a kerosene fired revelation kiln from 1897 in my basement. Used by my grandfather or maybe even great-grandfather. Would live to hear any information on it.

Gloria Valenti
Gloria Valenti

January 10, 2023

Is Pewabic pottery fired in an electric or gas kiln? I love your glazes. Thank you.

Anat Shiftan
Anat Shiftan

September 12, 2022

It would be lovely if you also mentioned the research Diana Pancioli did in the mid-1980 "s o reconstruct the luster glazes and achieve the reliable outcomes.
UI worked at the time as her research assistant.

Liz Mikols
Liz Mikols

August 30, 2022

Alex, You are looking good, decorating that pot! We were in Matt’s Clay bodies class. I still haven’t gotten that white stoneware body to not craze our studio glazes. Onward and upward! Best wishes, Liz

Jim Dalton
Jim Dalton

August 30, 2022

Great story. A determined woman.

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