Smalt is an artist's pigment seldom found in modern palettes or paint lines, despite  historically being one of the most important blue pigments, used by such titans of art history as Vermeer, Rembrandt, and J.M.W. Turner.

Most artists, if they are even familiar with Smalt at all, have at best a hazy notion of what it is, and what little is known is shaped by its use in oil painting, which, if you are a watercolorist, will offer a distorted view at best.  Even in artistic manuals, Smalt is often described only briefly as a blue glass pigment with unpredictable permanence, before moving on to describe the celebrity pigments of the archaic past or present in fawning detail.  However, there is some good reason for this ambiguity: much about Smalt's origins and chemical inner-workings have only been revealed recently. 

 

What Is Smalt?

Dry Smalt pigment on the slab at G&B studios.

 

Smalt is a blue glass pigment that receives its color from cobalt, and also contains potassium.  In chemical terms it is a Potassium Cobalt Silicate.  It is ground to different grades of coarseness, each of which deliver different degrees of blue, the coarsest grind offering the deepest blue and finer grinds being lighter and having less color.  However, larger pigment particles increase the difficulty of handling (though present different opportunities as well).

In terms of hue, Smalt is close to Ultramarine, but is lower chroma.  While it does transmit red light, it is not as red as Ultramarine, and therefore the hue differs slightly as well from Ultramarine (in addition to the chroma).

 

Smalt's Origin

In contrast to what was previously thought, Smalt is likely not of European origin, and was first made long before the sixteenth century, the time period previously attributed to its invention.

References to Smalt or zaffre, as it was known to glassmakers, can be found in texts from as early as 1144, 1301, and onward.

 

An example of Smalt used in a painting: Equestrian Portrait of Charles I by Van Dyck, 1638-9.  Smalt is used here in the sky, along with natural Ultramarine and Lead White in places.  Painting held by the National Gallery.

 

In the seventeenth century it became a substitute for Azurite and Lapis Lazuli when neither could be found, or if neither could be afforded.  As a pigment that could be synthesized (unlike either Azurite or Lapis Lazuli at that time) with relative ease, and was used in other popular trades such as ceramics, Smalt was plentiful and affordable.

 

Smalt's Name

Smalt in a Half-Pan.  The fact that it appears nearly black reveals its wide value range, but keeps a secret its transparency.

 

The name Smalt is from the Italian term smaltare, meaning 'to melt', though its etymological roots can be traced back much further.  Before the seventeenth century and the height of its use as an artist's pigment, Smalt may have been a term that merely referred to ceramic glazes (of any color) and/or various types of glass, causing no small degree of confusion when later adopted as a name for a specifically blue pigment.

Smalt has also been known under other names such as azurblau, Bohemian Blue, Dutch Ultramarine, enamel blue, Isenburg Blue, and, hilariously, émail, among many other names.  (Hilarity aside, émail translates to "enamel or glaze", and shares etymological roots with the term Smalt.)  It was also known by many as Saxon Blue since the primary sources of cobalt ore used to make it were located in Saxony.

Dry Smalt pigment.

 

Before synthetic Ultramarine was invented, Smalt was used to blue linens and was known as Powder Blue for that application.  It was known as Blue Sand in ceramics, and Dumont's Blue and Royal Blue for different grades of artist's pigments.

 

How Smalt Is Made

A detail from the Annaberg Mountain Altar, painted by Hans Hesse around 1500.  The altar painting depicts various aspects of ore mining work.

 

The process for making smalt has remained much the same since at least the late seventeenth century.  Cobalt ore, known as Smaltite, was mined in the Erzebirge ("Ore Mountains") of Saxony in conjunction with silver mining. 

To make Smalt, the first step is to roast the cobalt ore to remove the arsenic-containing vapors, leaving a residue which is cobalt oxide.  This is pulverized and sieved.  Next, this product is mixed with quartz sand, potash, and potassium, and  heated for a span of hours until it is melted and fused together as molten glass.  The vitrified (converted to glass) mass is then plunged into water to make it friable (easy to crumble), where it cracks into pieces that are then ground.  Then it is sieved again, ground further if need be, washed, and sorted according to color grade and coarseness of grind.

 

Smalt being made in Germany according to a nineteenth century recipe.  This is after the mixture has vitrified and is ready to be plunged into water.

 

Over time, the process became more standardized so that the particle size is the main determiner of the color, where previously unpredictable batch results would be the determining factor of the final color.

At the height of its use, it was being manufactured in the Netherlands, where it was of use in other industries too, most notably ceramics.

 

Handling Characteristics Of Smalt In Watercolor

This is our Combination Swatch of Smalt.  You can see from the black lines (the top drawn below the swatch, and the bottom drawn over it) that Smalt is very transparent.  Notice also the granulation it deomonstrates (painted on cold pressed Arches paper).  Because of the large pigment particle sizes it lifts beautifully, revealing white paper below.  See more swatches in our Overview of Pigments.

 

Smalt is notoriously transparent, and has a weak tinting strength, meaning it is easily overwhelmed by other colors when mixed.  It also has a wide value range, which because of its transparency, can only be accessed through the build-up of layers.  High quality Smalt pigment has a hue that is a deep, warm or violet blue, that can be by turns bright or haunting, depending on application.  Smalt also has a wonderful ability to granulate, a characteristic prized by many watercolorists.

 

This is a Value Range Swatch demonstrating Smalt's extremely wide value range.  If built up in layers, it can appear nearly black.  See our Value Scale Chart here.

 

Watercolor pigments with larger particle sized handle very differently from those that have very fine particles.  Today's synthetic pigments contain infinitesimally small particles, which, when combined with the dispersants that many watercolor manufacturers use, give a now-characteristic "bloom" effect that has become closely associated with watercolors.  Coarsely ground pigments will not disperse in these ways because the larger pigment particles will not be carried away either by the water or atomic forces in the same way as smaller particles.  As a result, these more coarsely ground pigments will exhibit more flocculation (it will feel as if the color wants to cling together or to your brush, rather than disperse).  This is not a pigment quality issue.  It is simply a physical reality.  Many pigments, including but not limited to Smalt, Malachite, and Azurite, exhibit strongest color when ground more coarsely, and will appear as very light or even transparent when ground as finely as one might wish for use in watercolors.

 

Smalt vs. Egyptian Blue

Smalt and Egyptian Blue can be somewhat conflated, both because of their similarities and because of Smalt's rather broad-reaching use (both as a term and a material) and because of its much-debated origins.

Egyptian Blue is also a blue glass pigment, but instead of receiving its blue color from cobalt ore, it receives it from copper.  Egyptian Blue is sometimes referred to as a smalt and/or categorized as as such.  It is the first known man-made blue pigment, while Smalt is the first pigment to contain cobalt (it was not until many, many years after Smalt was in use that cobalt was isolated and identified as an element).

 

Smalt vs. Thénard's Blue

Smalt predates Thénard's Blue by several to many hundreds of years, which turned up as a result of the French government's famed search for a synthetic version of Lapis Lazuli.  The Napoleonic administration appointed Louis-Jacques Thénard to find a substitute for Lapis Lazuli, and instead he found Cobalt Blue.  Cobalt had been identified as the coloring agent in Smalt by the early eighteenth century, but Thénard was the first to further isolate it to create a bluer pigment after he began his experiments in 1802.  It is a purer and more robust blue than Smalt, Azurite, Indigo, or Prussian Blue, was immediately adopted, and has been in continuous use ever since, though the process of making it has changed and evolved through the years.  Ultramarine would be synthesized by Jean-Baptiste Guimet in 1826.

 

The Waning Use Of Smalt

Our Peackock Set, a collection of both modern and historical blues.  from left to right, top to bottom: Australian Vivianite, Afghani Lapis Lazuli, Chilean Lapis Lazuli, Ultramarine Blue, Kazakh Azurite, Verditer, Yucatán Mayan Blue, Smalt, Phthalocyanine Cyan, Indanthrone Blue, YInMn Blue.  (As of yet we do not offer a Prussian Blue because it is low in chroma, easily mixable, and psychotically messy.)

 

Smalt's real heyday was from the sixteenth through eighteenth centuries.  Lapis and Azurite were preferred, but both were far more expensive and in much shorter supply.  Smalt, whether taken up with gratitude or grudge, was used prolifically, despite difficulties in handling and questionable permanence.  After Prussian Blue became available to artists in 1724 (after being synthesized for the first time in 1704 by Johann Diesbach), followed by Cobalt Blue in the 1820's, and then Ultramarine Blue in the 1850's, artists had little inducement to further trifle with the persnickety Smalt.

 

Toxicity

Smalt is considered mildly toxic because of its cobalt content.  Cobalt can be toxic if ingested or inhaled.  Inhalation is of greatest concern when handling the dry pigment.  Best practice for using Smalt is to wear a proper mask if handling the dry pigment and to avoid eating it, especially in large quantities.  While it isn't specifically listed as a skin irritant, it is always a good practice to keep paints off your skin.

 

Lightfastness of Smalt

Smalt has something of a reputation of being either very fugitive or completely unpredictable as a result of remarkable inconsistency within even the same (oil) painting: sometimes being wholly fugitive and other times very permanent.  This baffling misbehavior has only recently been understood to be a result of the potassium concentration in the pigment sample.  Smalt has been shown to not fade when the ratio of potassium to cobalt is 1:1 or higher.  The Smalt that we use has a ratio of 2:1 and is therefore considered permanent.

As a result of modern research and machinery, and a more standardized, better-understood production process, we have the supreme luxury of enjoying Smalt pigment of great quality, depth, and permanence.

 

Conclusion

 
This is a Flat Wash of our Smalt, its granulation on full display.

 

Just as the automotive industry drives the artist's pigment industry today, so too did oil painting dominate the art world of the seventeenth and eighteenth centuries, and therefore skews the literature.  It can be difficult when researching pigments, especially their applications, artist's opinions of them, and their availability, to remove the filter of oil painting, through which they are often viewed.  Smalt and linseed oil happen to share a nearly identical refractive index, making Smalt infuriatingly transparent in oil paint.  Further, oil has a particularly degrading effect on Smalt as a result of potassium leaching through saponification with the oil and the migration of cobalt ions into the oils.  Smalt would seem a downright curious choice for an oil painter if not for it being a well-known siccative (or drying agent), and, well, sometimes the only blue option available.  

Indeed, Smalt in watercolors is thankfully a different story altogether, and one worth noting.  Smalt is much more stable in water media, allowing it to sidestep the complications that oil media present, and shines in watercolor's unique ability to reveal the granulation of pigments.  While the coarser size of the pigment particles give it different handling characteristics than its finer brethren, its jewel-like hue and stunning granulation more than make up for its unwieldiness.  

 

As always, wishing you happy painting,