by Dwayne Anthony, NIA # 3619




Forgeries, fakes and physical alterations appear to be an escalating concern for nearly all categories of collectibles and antiquities. The esteemed hobby of insulator collecting is, unfortunately, no exception. Of particular concern is the recent escalation of color-altered insulators appearing primarily at flea markets, antique shops, antique/collectible shows and public Internet auctions. The alterations discussed here are not by external application of paint, stains or dyes. They are a more technical modification to the internal ingredients of the glass itself. 


There are two sources known for intentionally altering the integral color of glass insulators: thermal and radiation. Both can create color changes from very subtle to extremely radical. Thermal alterations, as the term implies, are achieved by use of extreme heat. Alterations performed by use of radiation sources are much more complex and include high levels of gamma rays and electron beams. When any form of the word “altered” is used in this report, it applies only to alterations produced by radiation and/or thermal exposure.


The National Insulator Association provides funding for an ongoing research and experimental program involving the altering of certain targeted insulator specimens. Whenever possible, damaged specimens are used. The results of these experiments are documented and select specimens become part of a traveling exhibit that is shipped to insulator shows across the country for educational purposes, complete with free handout copies of this report. Most of the information in this report is based on the outcome of these research experiments. Please be aware that our research is ongoing and may be updated at any time, especially any information presented below that is currently deemed inconclusive.



Why alter insulator colors?     

You may be wondering, “What benefits could possibly be gleaned from altering an insulator’s color?” In most cases it is simply shrewd greed. There’s been a recent proliferation of irradiated insulators offered on eBay, some in very striking and previously unknown colors. Even though some of the listings declare the insulators as altered, the foremost objective of these fake insulator peddlers is immediate profit, with no regard for the long-lasting harm being perpetrated upon our hobby.


Let’s look at a couple of examples of how greed affects our hobby: A simple CD 145 beehive insulator, embossed Postal, aqua in color, can commonly be found for sale in the $1-3 range. The exact same insulator subjected to radiation and altered to a stunning sapphire blue color was sold to an unsuspecting collector for $500. A CD 151 embossed H.G. Co. Petticoat, light aqua in color, can be purchased in the $1-3 range. The same insulator altered to a grayish cornflower blue was sold to an unsuspecting collector for over $200.


Some collectors have been known to alter insulators for “fun”, as novelties to add to their personal collection. This is highly discouraged as an unethical practice by the National Insulator Association. Many insulators that were color altered as “fun novelties” in the late 1960's and early 1970's have since lost their traceable pedigree. As a result, a fair number of these transformed insulators have been sold by, and sold to, unsuspecting collectors as authentic specimens for hundreds, possibly thousands of dollars!


  How do the colors change?

The primary ingredients for making raw glass are: silica sand, soda ash and limestone. Iron is almost always naturally present in silica sand, providing a light to medium blue green color to raw glass. Raw glass was customarily referred to in the glass making industry as “green glass” due to this iron-induced color. Within the hobby of insulator collecting this same “green glass” color is generally referred to as “aqua”. A variety of additives can be added to glass to create specific colors, or in some applications additives are actually used to neutralize the natural aqua shades so our eyes see colorless glass.


It was common practice in the manufacture of glass insulators to add a generous percentage of cullet to each batch of raw glass. Cullet, a term used for recycled glass, allowed for a lower melting point, which in turn provided a savings in energy use. The cullet--sometimes sorted by color, sometimes not--provided an unmeasured blend of ingredients and coloring agents that made each glass batch unique. In some instances the coloring agents within the cullet were significantly diluted or nullified when added to the raw aqua “green glass” and produced very little to no discernible color changes to the final product. However, when this same aqua glass is exposed to radiation or heat, these “hidden” ingredients become the influential factors in any color transformations that might occur.


All insulators exposed to radiation and/or heat will not progress to a new color. Only those with select ingredients contained within the glass will change colors, or deepen in color. One very important point to keep in mind is that color changes are not always excessive. Under controlled situations, the slightest of color tone changes are possible. A CD 121 toll, embossed WFG Denver Colo was altered from its original color of light lavender to dark strawberry puce, then lightly reversed to a vivid dark purple, then again to a medium shade of purple. Any shade within the original light lavender to the dark puce range could be attained with careful management of the altering process.


The actual scientific explanation for what occurs during a color change is far too technical and complex for a brief and accurate detailing here. These phenomena involve electron energy levels of atoms or defects in the glass structure, which are created or modified by radiation and annealed by heat. These sites absorb or emit light at specific wavelengths, which our eyes perceive as color. If the reader has an interest in obtaining specific and detailed information on these fascinating topics they can be researched on the Internet or at your local library.


Are all altered colors easily recognizable?  

Not always. Educated collectors can usually clearly identify the most obvious of the altered colors, those that are too dark, too wildly colored or display a distinctive “burnt” appearance to the color. However, if not always on their guard, there are alterations appearing on the market today that can certainly deceive even the most advanced and knowledgeable of collectors. The key is education and awareness. 


 1.  “Natural” Color Transformations (Sun-Purpled Glass):  


Purple, or “sun colored amethyst” is a popular color with glass collectors. Many of the purple shades we see in various insulator styles are actually secondary color transformations from their original color, the result of a natural color altering process brought on by prolonged exposure to sunlight. In some glass collecting circles, clear glass that has been sun purpled is looked upon with disgrace and is unacceptable. Because sun colored purple is the result of a natural transformation that occurred during an insulator’s time in service, this is the only form of color altering that is entirely acceptable within the hobby of insulator collecting. It is important that we examine this natural process that transforms some forms of glass to purple, allowing the reader to develop a better understanding of the artificial forms of color alterations subsequently following in this report.

The principal additive in glass that produces these varying shades of purple is manganese. Manganese, when measured properly, was used as a clarifying agent in glass to neutralize the blue-green coloring effects of the naturally occurring iron impurities in raw glass, thus producing a clear or off-clear glass (at least as we perceive it within the wavelength that reaches our eye). Manganese is a sensitive reactor to electromagnetic radiation. Within the scope of electromagnetic radiation there is a low level amount emitted by our sun in the form of ultra violet light. Over a prolonged period of time, moderate to higher levels of manganese in glass will react to the ultra violet light from the sun, causing a “purpling” effect. Dependant upon the levels of manganese in the glass, this purpling or solarization can produce multiple graduations in color from a pink tint to moderately dark purple.


If the manganese content in the glass occurred from cullet, the proportions would likely be incorrect for clarifying, allowing the iron and/or other ingredients in the cullet to bleed through and produce some form of color. Although not visibly apparent, many aqua insulators contain some degree of manganese below the required amount for them to purple by sunlight. It is most probable that a good amount of the manganese content found in glass insulators was derived from the large amount of cullet commonly used for their manufacture. As a result, this “bleeding” created certain specific original insulator colors that although not clear, were still susceptible to purpling by the sun. An example would be the varying shades of yellow, green-tinted yellow and golden yellow shades found in California embossed insulators; and the off-clear, straw and lime green shades found in WGM insulators.


When an extreme level of manganese is present in glass, original shades (prior to sun exposure) of dark purple can result. In some cases, when the manganese level was accurately measured, the insulators were produced in clear to off-clear glass. Selenium replaced manganese as a glass-clarifying ingredient during the World War I period. However, manganese continued to occur in some insulators for several years longer as manufacturers repeatedly added manganese-rich cullet to their glass batches. 


It is of interest to note here that a multitude of color shade variations can occur during a sun-induced, ultra violet transformation period. The popular “peach” color occasionally found in WGM and California embossed insulators is actually a mid-transformation color from yellow to purple. These insulators were evidently used in sheltered areas where very little direct sunlight was cast upon them. Some examples display a two-tone effect that resulted from one portion of the insulator having a stronger exposure, such as placements near a building, partially under a roof eave or in heavily forested areas. Manganese-rich insulators that were used indoors or in completely sheltered areas remained their original color.


2.    Thermal Reversals of Authentic Colors (Reversing Sun-Purpled Insulators):

It is an established certainty that most, if not all, light to medium purple California embossed insulators emerged from their factory molds in shades of off-clear, yellow, smoky yellow or light yellow green; and the darker purple/deep burgundy examples were most likely golden yellow. Light to medium purple WGM insulators were originally clear, off-clear, straw or light yellow green. Since we’ve already learned that manganese-bearing glass will react to the ultra-violet rays of the sun, we now know how and why the preceding examples were naturally transformed to varying shades of purple. We will now investigate a practice that has been performed by some unscrupulous individuals to reverse this natural purpling process, in some instances for monetary gain due to the rarer and more valuable resultant colors.  


Exposure to high levels of heat will reverse the sun’s ultra-violet purpling effects on glass. This procedure is often referred to by collectors as “cooking”. During the thermal reversal or “cooking” process, the manganese is once again the key stimulant. In most cases, when a sun “purpled” insulator is heated to high temperatures, generally a step below melting, it will revert back to a shade in close proximity to its original manufactured color.   By Reintroducing a "cooked" insulator to direct sunlight the natural purpling process will begin to occur once again, although the resultant color tones may differ from the original.  Be aware that deliberate partial exposures can create artificial two-tones as well.

With all this in mind, we are now faced with the paradoxical question: Should “cooked” insulators really be considered fakes? Unlike an irradiated insulator that is transformed to a fake fantasy color, cooked insulators most often appear similar, if not exactly, as their previous original color. However, when it is ascertained that an insulator has been purposely color reversed by unnaturally applying heat, it is no longer considered a “factory original”. Given the information presented here, some may argue that an insulator cooked back to, or similar to, its original color may not be an actual “fake”, preferring terms such as “altered” or even “restored”. To some extent this might be true, but there’s no disputing the fact that any insulator becomes an impostor when it is artificially altered from its naturally occurring state. Regardless of which term you feel is most appropriate, “fake”, “altered” or “restored”, all insulators unquestionably identified as cooked are considered counterfeits and should no longer hold any appreciable or historical value within our hobby.


View photographs  View photographs of some examples


3.         Radiation Exposure (Producing Fantasy and Imitation Colors):

Gamma rays and electron beams are the primary sources for irradiating insulators. Cobalt-60 and Cesium-137 appear to be the most popular and current “weapons of choice”. Those with access to such facilities containing these radioactive isotopes have the potential to expose hundreds, possibly thousands of insulators to radiation on a daily basis!


Manganese is highly excitable when exposed to intense radiation sources. A very small quantity of manganese contained in an aqua insulator, most likely from cullet usage, can produce dense, dark purple tones when exposed to high levels of radiation. In addition to manganese, there are myriads of other glass impurities and additives found in insulators that are susceptible to color changes when exposed to radiation. Some color changes are radical, others can be slight. Some are easily identifiable, many are not. These seemingly endless variations in color changes are, again, brought on by indiscriminate cullet usage in early insulator manufacturing.


Not all glass insulators will react to radiation exposure. Our experiments have seen a good number of specimens appear unaffected after a trip to the radiation chamber. In addition, it is of great interest to note that two authentic insulators of the same style and appearing identical in color to the human eye can be exposed to radiation and emerge with completely different results. For instance, let’s take what appears to be two identical insulator specimens in light aqua glass and expose them to equal doses of Cobalt 60 radiation. The first sample emerges from the chamber with absolutely no discernible changes; however the second sample has transformed to a dark purple. How is this possible? Even though the two samples appeared identical, they were obviously from two separate glass batches. This brings us back to cullet usage, which apparently varied with each glass batch. No two scoops of unsorted cullet will be identical in mineral and impurity content, giving each new glass batch a uniqueness of its own. This is an important point to remember if comparing the color of a suspect insulator with a known irradiated sample of the same type and style. Just because the colors are not a match does not give immunity to the suspect specimen—the shade variances can be unlimited.


Of real concern are the irradiated insulators that exhibit similar, if not exact color similarities to authentic specimens. This mock similarity occurs typically in, but not limited to, varying shades of purple and some shades of blue, including sapphire and cornflower. In such instances, verifiable pedigree may be most advantageous in identifying authenticity. These impersonating fakes can also be fashioned by yet another secondary form of altering. Please read on…  


View photographs  View photographs of some examples


4.         Thermal Reversals of Irradiated Insulators (Low Level Heat Reversals):

We have heard and read conflicting reports that irradiated glass will reverse back to its original color upon exposure to heat and/or light. Our ongoing experiments have only provided partial support to such statements. While this may be true with the more modern types of glass, we have seen very mixed results with older insulator glass. Heat seems to be the primary factor when attempting to reverse irradiated insulators. We have not seen any perceptible effects of prolonged exposure to light alone on any of our irradiated samples. Prolonged exposure to sunlight or being in very close proximity to a lamp’s light bulb has provided some reversals, but these methods also involve heat exposure, so it is our belief that thermal exposure is the key element to any possible color reversals, not light alone. There have been reports that irradiated insulators left undisturbed on a windowsill exhibited fading on the exterior exposure side, with no change on the interior side. Both sides were exposed to light, but the exterior side experienced heat transmission through the glass when direct sunlight passed across the window on a daily basis.


Our attempts to reverse irradiated insulators with lower levels of heat have been met with varied results. (Higher levels of heat exposure are addressed in the next and final category of alterations.) “Lower levels” of heat include prolonged periods in a standard kitchen oven, and/or many cumulative months of exposure to the hot summer days of Inland Southern California. Most of the brown amber irradiated shades tend to reverse or partially reverse fairly rapidly. The deeper purple shades can be problematic, with some showing moderate partial reversal times, while others refuse to weaken at all with very long exposures to oven and/or solar heat.


It should be noted at this point that a number of insulator specimens that we successfully reversed did not revert back completely to their original colors. Some seemed to stop shy of a full reversal, retaining a light tint of the irradiated color. These tints can create unusual and sometimes unique color variations that are not easily identifiable. Specialists collecting shade differences should be extremely careful when unusual, undocumented color variations appear with no valid documentation.   


There are other sporadic anomalies with reversals that also should be noted.  We have observed a two-tone affect in a small number of partially reversed specimens.  In such cases, certain areas of the glass fade much quicker than others, leaving a distinctive two-tone appearance.  In one extreme instance a cracked dome-top of an irradiated purple WFG toll was removed and reversed back to its original aqua color, then expertly glued back into place, creating a simulated two-tone effect.  Swirling color patterns can also occur if the insulator originally contained two-tone swirls, milk or amber swirls.


5.         Thermal Alterations of Irradiated Insulators (Secondary Higher Level Heat Alterations):

Our final category of alterations involves exposing irradiated insulators to high levels of heat. In some instances this creates a secondary altered color, much different in appearance to the primary irradiated color. During one of our numerous experimental procedures, one particular pony insulator was first altered from its original color of light blue aqua to a burnt olive brown. This same insulator was then subjected to extreme thermal exposure, transforming to a medium shade of cornflower blue.


We know that some of the unscrupulous new era “nukers” are using this same process to dial in colors that very closely mimic authentic insulator colors, and with considerable accuracy. Even though such color duplications look authentic, they are, of course, outright frauds. These “chameleons” can be very difficult to identify.

 Are there any reliable methods for positively identifying altered insulators?


For the most part, there is no easy way to identify the majority of thermally reversed purple insulators that have appeared in our hobby. Slumping glass, rack marks or flattening on the base are possible indicators that an insulator was reheated, but positive conclusions cannot be drawn since many authentic insulators exhibit similar characteristics. However, if combinations of these characteristics are apparent on a single specimen, it certainly adds more suspicion of thermal color manipulation. To narrow the field of possible examples, the majority of “cooked” purple insulators present in the hobby today are embossed California, or WGM Co.  Other varieties known, but not as prevalent, are: Am Tel & Tel, BGM Co, Good, Hemingray & Postal. Experimentation has proven that several additional embossed and unembossed types are potential candidates. Basically, any insulator encountered in shades of clear, off-clear, straw, yellow or light yellow green that are also known to exist in light to medium shades of purple, hold the potential of being cooked. The deep royal purple WGM’s are thought by some to have been originally burgundy, but this is disputed in some circles due to the lack of documentation of an original burgundy WGM being found in the wild.


With a little education, a fairly accurate visual identification can be achieved within a select group of irradiated insulator colors and types. This generally applies to those that are altered in color or shade well beyond their known authentic counterparts. This might include documented types that were only produced in clear, aqua, or light green, suddenly appearing on the market in royal purple or dark brownish amber. Some of the darker irradiated purples tend to contain vivid bluish hues, which in some cases might assist identification, but unfortunately we have also seen many exceptions to this rule, as well. To a relatively experienced eye, the browns and muddy olive browns created by radiation exposure are reasonably easy to identify. As for the many other colors and shades, it can get very difficult to make distinctions between real and fake.


There’s one form of testing you might attempt with suspected irradiated insulators. Expose them to the direct heat of the summer sun. This may require as little as a month or two, or possibly several months or even years to see partial to substantial results.  If an irradiated insulator tested in this manner begins to show signs of reversal, you have solved the mystery. Unfortunately, if the color remains unchanged, authenticity is not necessarily substantiated, since the altered colors of many irradiated insulators tested thus far have proven to remain stable.


We are currently looking at a possible method for identifying irradiated insulators that fall within a specific color range. As we know, natural purple or sun colored purple glass insulators contain manganese. Generally, the darker the purple the more manganese content in the glass.  Manganese is very sensitive under a black light, providing a yellow to greenish yellow glow. The glowing intensity of authentic purple insulators is fairly easy to measure with the human eye, particularly after viewing several examples with a long wave black light in a completely dark room. We have found that most irradiated purple insulators display a diminished glow when compared to authentic purples. We have also noted that some of our insulator samples exhibited good black light glowing characteristics prior to radiation exposure, then deadened under a black light after radiation exposure. We are continuing our testing with this method and hope to have more validated and expanded information in the near future.  


Radiation will still alter insulators with heavy dirt and soot accumulations on insulators, so don't assume a possible suspect color is authentic just because the insulator retains its original soiled appearance.



The purpose of this report is not to create paranoia, but to make today’s collector aware through education that the technology exists for altering natural colors of genuine old glass insulators. Your best protection is to be educated and investigate the source of any unusual color. If you happen upon an insulator you feel falls within the suspect category, always be suspicious and ask questions. Beware of anyone that might avoid your questioning or use the “playing dumb” act, especially if they have multiple quantities of suspicious items. Any ethical collector or dealer will welcome questioning and should provide sufficient answers and/or documentation. Most important of all, go with your instincts!


The National Insulator Association has adopted a set of guidelines for insulator collectors known as the NIA Code of Ethics. These guidelines were established for members and non-members alike to set a standard for conducting all collecting and dealing activities honorably and honestly.


Regardless of the occasional “questionable insulator” encounter, this is still one of the greatest hobbies on earth! May your continued collecting prove enjoyable and rewarding!  


List of known altered colors


View photographs  Photographs of radiation induced purple insulators


View photographs  Photographs of radiation induced insulators (blues, greens & ambers).


View photographs  Photographs of Thermally altered insulators


(Presentation and funding of the ALTERED INSULATORS EXHIBIT and this ARTIFICIALLY INDUCED COLORS  REPORT is made possible by the National Insulator Association, with development, research and maintenance by Dwayne Anthony.) [Last revised 01/06]


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