Dyed Stones - Agate, Howlite, Quartz and More
These brightly-colored tumbled stones are dyed agate. Before dying they were a uniform white or milky gray color.
What Are Dyed Gemstones?
Dyed gemstones are stones that have been treated with a dye to alter their color. The purpose of the color alteration is to increase their visual appeal or marketability. The stones selected for dye treatment are usually those that are nice gemstones in every way, but they simply have a color that is plain, weak or uninteresting.
Lapidaries (people who work with gem materials and ornamental stones) have used a wide variety of methods to change the color of stones for thousands of years. In Book 37 of his Natural History, written nearly 2,000 years ago, Pliny explained how ancient lapidaries boiled gemstones in honey as part of the process of changing their color. Dye and many other methods such as heating and irradiation have been used to change the color of many types of stones.
Granite that contains an abundance of white feldspar readily accepts dye to produce brightly-colored tumbled stones. Most people would never guess that these colorful stones are granite.
Recognizing Dyed Tumbled Stones
Dyed tumbled stones are often such bright or unnatural colors that people who are familiar with tumbled stones will recognized them immediately. The use of dye can also be detected if the color is darker in fractures, pits and areas of low relief. Dye tends to accumulate in these areas, while at the same time being lighter on areas of positive relief.
In most cases a dyed stone has a brightly colored surface but the dye has not penetrated deep into the stone. For these stones, scratches or chips often reveal an interior where the color is lighter or undyed. You can also break a stone, scratch through its surface or touch it against a grinding wheel to see if the interior is undyed.
Although most dyed stones are easily recognized, experienced persons can be fooled when the color is closely matched to a natural material. The first specimens of dyed howlite produced were a beautiful turquoise blue color. Lots of smart people thought they were genuine turquoise. Lots of people are still fooled by dyed howlite.
Informing Potential Customers
When dyed gemstones are offered for sale, potential buyers should be informed that dye has been used to modify their colors. About 40% of the stones in our Souvenir Mix have been dyed. Photos of dyed howlite, crackle quartz, dalmatian stone, feldspar and granite - the dyed stones most often found in our Souvenir Mix can be seen on the right side of this page and are included on our tumbled stone identification chart.
Howlite is one of the most frequently dyed stones. It is popular for use in making tumbled stones, many types of beads and other items. Howlite is a white stone that readily accepts dye with predictable color results. It is often dyed bright blue colors to resemble turquoise.
What Types of Tumbled Stones are Dyed?
The types of tumbled stones that are often dyed include: howlite, agate, dalmatian stone, feldspar, jasper, quartz and granite. We have posted photos of dyed specimens for each of these types of stones in the right column of this page. The characteristics of these stones that make them favorable for dying are explained below.
Howlite is an excellent material for making dyed tumbled stones. It is usually a bright white color that faithfully assumes the coloration of a dye. It is also a softer mineral (3 1/2 on the Mohs Scale). Because howlite is so soft it shapes and sands quickly in a tumbler, and it is still hard enough to accept a moderately bright polish.
The quick shaping saves electricity in the tumbler, enables increased factory throughput, reduces labor and saves grit. All of these savings make dyed howlite much less expensive to produce than the cost of tumbling a harder alternative material.
Dalmatian stone readily accepts dye to produce brightly colored stones with black spots.
The material used to make the lapidary material known as dalmatian stone is a white igneous rock with contrasting black amphibole crystals. The white matrix is composed mainly of albite, a plagioclase feldspar. The plagioclase is white and readily accepts dye with faithful color reproduction. The plagioclase is also soft (6 on the Mohs Scale) compared to the typically tumbled agate, jasper and quartz (7 on the Mohs Scale). As a result, dalmatian stone is very economical to tumble and dyes with great results. The resulting tumbled stones are brightly colored with large black spots.
Crackle quartz is produced by heating clear quartz, quenching it in a cool dye solution, and allowing it to soak. The quenching produces tiny cracks within the quartz which serve as conduits for the entry of dye. The cracks allow the dye to penetrate deep into the stone. The result is a transparent colored stone with bright internal reflections produced by the interaction of light with the tiny fractures.
Many types of light-colored feldspar can be dyed with faithful color reproduction. The dye seems to penetrate deep into the rock along tiny cleavage planes.
With a Mohs hardness of 6, feldspar is softer than the quartz, agate and jasper that is typically processed in a commercial tumbler so they can be tumbled in less time and at a much lower cost. These materials also crush easily into blocky fragments that can quickly be tumbled into nicely shaped stones. White feldspars such as microcline and albite are easily penetrated by dye to produce stones of predictable color. That is why dyed feldspar is sometimes seen in tumbled stone mixtures.
Granite is an unexpected stone to see in tumbled stone mixtures, however, when it is dyed it can be colorful and attractive. Those granites that are white and composed primarily of feldspar can be quickly tumbled and easily dyed to produce nice tumbled stones.
These stones are banded agate that has been dyed. Each band has a slightly different permeability and accepts different amounts of dye. That is what causes the color variations. Before dye treatment these stones were likely less interesting shades of white to light gray.
Agate is one of the most widely dyed stones. The bands often have different levels of permeability and that leads to different dye intensities within a single stone. No time is saved in the tumbling process so dyed agate is not always well represented in tumbled stone mixtures. However, the attractive color-banded stone is very popular in beads, bookends, slabs, and many ornamental objects.
The Dying Process
Dying is done after the stones are tumbled rather than dying rough materials. This produces the best results as the dye usually does not penetrate deeply into the stones. After the stones are tumbled they are placed in vats of dye and allowed to soak for up to several weeks. That amount of time allows the dye to penetrate the stone and produce uniform surface color.
Crackle quartz is produced by heating clear quartz and quenching it in a cool dye solution. The result is a stone with numerous tiny cracks that allow dye to penetrate deep within the stone. The tiny cracks produce internal reflections within the stone to give it a sparkly, glittery appearance.
Why Stones Are Dyed
The photos in the right column show how colorful dyed stones can be. Although many of the colors are not typical of any natural-color material they are spectacular, attractive and appeal strongly to some people. These are the advantages of dyed stones for the consumer.
The manufacturer benefits because dyed stones can be produced using rough that is abundant and otherwise would be of limited commercial value. Because most of the materials used for dyed stones are relatively soft and tumble quickly they can be processed into tumbled stones with less labor, lower cost and with a higher factory throughput. Dyed stones are also purchased by some people who would not have purchased stones with a natural color, thus increasing sales. These are the advantages of dyed stones for the manufacturer.