Artificially Purpled Glass / Irradiated Glass / Altered Glass

Artificially Purpled Glass / Irradiated Glass / Surface-Stained Glass / Altered Glass

In recent years the practice of altering the color of glass has reached epidemic proportions, and is an increasingly confusing and undeniably damaging aspect of the subject of collecting antique or vintage glassware.  The fields of American antique bottles, Fruit jars, Early American Pattern Glass, and antique glass electrical insulators have probably been affected by this trend the most, but other fields of collecting are increasingly being affected too.

There are several ways in which glass can be color-altered, but the most common, as well as problematic, and highly controversial, is the use of equipment that sends germ-killing X-rays or Cobalt-60  gamma rays through food (including fresh produce and spices), killing micro-organisms as part of increased safety procedures. This process of irradiation (often called “nuking”) has been rapidly increasing in use in the United States over the last few years.

Purple (Amethyst) Glass

Authentic purple glass has been made for many years, and has seen periods of rising and falling popularity, particularly as relating to glass tableware. Glass lumped under the term “purple” can range widely from a very pale lavendar, to medium shades of purple, to very deep royal purple, to virtual “blackglass” in which the color can only be seen when a very, very thin sliver is held up to a bright light.

Much of the “clear” or “off-clear” glass made during the 1880s-1920s contains the element Manganese, which was actually added to the glass “batch” as a decolorizing agent. The manganese helped to “mask” or “neutralize” the effects of iron which typically causes some shade of light green, blue-green or aqua color in glass.

Manganese, in somewhat higher quantities, also imparts a purple color to glass. When manganese-containing types of glass are subjected to later irradiation, the glass may turn various shades of purple. These shades may appear as an odd “grape-Kool-Aid” purple, a blue-purple (almost leaning toward a cobalt-blue color in some instances) or a very deep royal purple.

Glass containing enough manganese may NATURALLY slowly turn some shade of very light to medium purple after several years of exposure to the rays of the sun. This was frequently termed “SCA” (sun-colored-amethyst) or “desert glass” by bottle collectors especially in the 1960s and 1970s. In most cases the shade of color is quite light or “pastel”.  HOWEVER, the artificial purpling of glass (especially when strong doses of irradiation is used)  usually causes a darker or “peculiar” shade of purple to result.


There are several fields of glass collecting in which the scourge of artificially “purpling” glass has become really a serious problem, especially to those collectors who have a real interest in the preservation of the history and integrity of old glassware. This includes the field of what is called  EAPG (Early American Pattern Glass) . Some of these pieces are artificially purpled and offered for sale at flea market booths and on online auction sites.  Such items as water and milk pitchers, spoonholders, creamers, tumblers, salt cellars, sugar bowls, compotes, cake plates, oil lamps,  and other forms of tableware in various patterns of the 1880s-1910s have been irradiated, and are sold to unwary collectors, or casual buyers merely looking for decorator items or something that “catches their eye”.  Some of these buyers really couldn’t care less about the provenance or authenticity of the glass, thus compounding the problem. If/when the nuked glass is re-sold later on, the next purchaser typically assumes the glass was made that color in the beginning.

Although some purple glass was produced in a few EAPG patterns, very, very little of it was made originally, in comparison to the TREMENDOUS quantities of clear (or an attempt to be as colorless as possible) early American glass tableware.

Bottle Purpling

Another field of glass collecting is the study and collection of antique bottles and flasks. Many of the more common types of clear glass bottles of the 1880-1920 period are now being mass-irradiated and sold at flea markets. If you spot a large number of old purple bottles (or jars) within a particular booth in a flea market or antique mall, you can be quite sure they have been irradiated, and were originally colorless, or nearly clear glass.

Irradiated "Sanford's" Ink jar, circa 1910s-1920s. This would have originally been in clear glass or with a slight amethyst tint.

Irradiated “Sanford’s” Ink jar, circa 1910s-1920s. This would have originally been in clear glass or with a very light amethyst tint.

The perpetrators of this type of wholesale altering of glass usually (but not always) do this to alot of the more unremarkable clear glass bottles such as common druggist, soda, ink, chemical, whiskey and food bottles, sometimes those with no brand name or city on the face, and often examples that are completely “slick” with no markings at all.
It is very common for old purple bottles such as these to be dull and heavily stained with a whitish residue or “sickness” on the surface of the glass. This is a very strong indication that the bottles have been dug (the sickness caused by long burial) , were clear to begin with,  and were later irradiated en masse.   Contrary to what some sellers might say, there is no reason to believe that these bottles would eventually darken to that degree if they were left in the sun for a thousand years. The process of irradiation is not quite the same as ordinary sunlight, and it is more likely that the glass would never attain this dark of shade of purple if purely “sun-colored” naturally.

Composite photo of irradiated glass from various sources (pic courtesy of Marianne Dow).

Composite photo of irradiated glass from various sources (pic courtesy of Marianne Dow).


Glass Insulators

Some glass telephone insulators, and some bottles which were originally an aqua or light green color may be altered/irradiated to come out a purple color, and in some cases (depending on the exact chemistry of the glass and what ingredients were contained in the cullet used when forming the batch) a peculiar cornflower blue, dull gray blue, or sapphire blue may result.

Two "AM TEL & TEL CO" insulators made by Brookfield Glass Company for AT&T CO in the 1900s-1910s. The piece on left is the natural as-found aqua color. The example on RIGHT has been irradiated which has produced an odd "cornflower" or "dingy sapphire" blue shade.

Two “AM TEL & TEL CO” toll insulators made by Brookfield Glass Company for AT&T CO in the 1900s-1910s. The piece on left is the natural as-found aqua color. The example on RIGHT has been irradiated which has produced an odd “cornflower” or “dingy sapphire” blue shade.


(To make this even more confusing, many types of insulators are found in shades of purple glass that are known to be authentic __ as found __ for instance some of the W.F.G.CO. and W.G.M.CO. insulators from Denver; the AM TEL & TEL CO tolls; the Whitall Tatum CO. No 1; and many of the “Diamond” CD 102 ponies from Canada).


Clear glass that was originally decolorized by using selenium as the active ingredient instead of manganese (the use of selenium was particular prevalent in the 1920s and 1930s and later) may turn strange shades of “burnt amber” or “smoky dull dark brown” under irradiation, which are colors virtually unknown in the production of the original glass product.  Just for an example: If you find an insulator marked “HEMINGRAY-42” and it is in a dark brown/amber color, it has been IRRADIATED! (No original Hemingray-42’s were ever made in such a color).

Recently, Coca-Cola and other types of soda bottles have appeared for sale online that have been irradiated, resulting in a peculiar ‘dull’ burnt brown shade.  The original “Coke bottle green” (light green-aqua) has been changed to this sickly appearance.

Knowledge of exactly which colors are known in the various types of original insulators can be gained by studying value guides, along with searching for information on various webpages that delve into more detail on this subject.  Sometimes, just the exact embossing arrangement (lettering on the glass surface) seen on a particular piece can make a big difference on whether a color is authentic or not.

“Stained Glass” / Surface-stained glass  (this subject is not pertaining to the more commonly understood context of “stained glass” as relating to architectural or ornamental glass seen in church windows)

Sometimes glass (and this pertains especially to electrical insulators) is surface stained to achieve the appearance of a different color, typically an unusual color completely different from the actual color of the glass. This has become increasingly common on auction sites such as ebay.   In many cases the description of the insulator is written in such a way as to deceive or confuse new or unsuspecting collectors who will assume a color is authentic or “all-the-way-through-the-glass” when it is merely a surface coating. A clear glass insulator of a common type with little monetary value may appear to be a much more valuable type by adding a surface coating!!!  The color may be achieved by using some type of glass paint, and sometimes subsequent heating to cause the color stain to adhere more steadfastly to the glass. Thus a “one dollar” insulator may be wrongly assumed to be worth much more because the color is perceived to be “rare”.

Most “serious” insulator collectors frown on this practice and encourage other hobbyists to learn more about what they are actually buying.   Some online sellers may imply in their descriptions that this practice of surface-staining is ethical or highly to be praised, and that the buyer is just obtaining an unusually colored insulator to display in their window for mere decoration.

There may be nothing intrinsically “wrong” with that, but the problem comes when the piece is RESOLD and the next person who gets it may have NO IDEAS on it’s provenance or whether or not the color is authentic and original. The insulator may be sold for a much higher price than it is worth, if either the seller and/or the buyer doesn’t understand that the color is entirely FAKE.

Here are some webpages that I would strongly recommend for more detailed information on this subject~~~

Artificially purpled Early American Pattern Glass:

Webpages concerning fake and altered glass insulators:

Fake colors in insulators:

Bottle colors: to Amethyst

Bottles — Irradiated Glass, the Color of Greed:

A nice reference book illustrating lots of purple glass:

Purple Glass: 20th Century American & European, a Schiffer Book for Collectors, (Leslie Pia,  Ed Goshe and Ruth Hemminger)  illustrates a wide variety of purple tableware and art glass, all (or virtually all) believed to be authentic and as originally made.

Please click here to go to my Home Page.

Click here to go directly to the Glass Bottle Marks pages (listings of marks used by glass companies / manufacturers on bottles and other glassware).

16 Responses to Artificially Purpled Glass / Irradiated Glass / Altered Glass

  1. Dan says:

    All right bud I got one problem with you and what you’re saying they’re fake glass changing colors green purple midnight all this b******* that you keep talking about like you know what you’re actually talking about I don’t think you know crap. yeah they make s*** in a certain color you know what there’s nothing fake about it,……….and all that you know and what you said downgrading something that’s rare or unique are fake I think that’s crap and I think what you’re saying is crap just cuz you’re not made right what you say doesn’t mean crap you are a fake you don’t understand anything I realize that now I read your comments on everything and I think you are an idiot. Aged glass patina makes things different that’s what makes them rare you act like people are making them to make them rare and more valuable I think that is the most idiotic thing I have ever read thanks happen naturally that makes him a fake things change colors through age that makes them unique patina is a natural occurrence it does not make it fake takes years to make something change its color like that . And it takes an idiot to actually say the bulshit he just said just because it’s not in its original state does not mean it’s a fake

    • David says:

      Hi Dan,
      Since this is a free country (so far), you are welcome to say and believe anything you want to. I will admit that there are many purple bottles, jars and other glassware that were made in a purple color (to begin with) and have always been that color from the beginning. They are not fake. But this article isn’t really about that. I am referring to the types of glass that have been changed by irradiation to a different color than what they were when first made at the factory.
      “Patina” is a whole different ball game. Glass with a ‘sick glass’ Patina, like “Bernicia Glass” can have that beautiful rainbow color, sorta like gasoline sheen on a mud puddle. Not sure what you mean by “patina” but this article isn’t about glass with a patina, but a color change that goes all the way through the glass. “Patina’ is just a surface change.

      Most of the altered-color items (such as insulators, bottles, EAPG kerosene lamps) are not fake……. yes, they are real, original glass items, but they have had their original *color* changed. “Fake” is a word that is used by many people with a lot of slightly different definitions. Collectors who like to know how old their glass is, and what the original color was, might be inclined to call an altered-glass item a “fake” even though, technically, it is real. Just the fact that the color is not “original” is enough to have it classed as a “fake” by some collectors.

  2. says:

    I found a dark amethyst double safety jar at an antique store. I’m guessing it was irradiated to be this dark? It caught my attention as it was so dark. They were asking 70$ so I thought I’d do a bit of research here first! I wasn’t aware of irradiating old glass!

    • David says:

      Hi Darlene, and I am glad you checked out my article. Yes, it is an irradiated jar. Practically NO fruit jars were made in purple/amethyst glass, so we can be sure the color has been changed by artificial means. Take care,

  3. Pingback: What is Amethyst Glass? – The Curious Phoenix

  4. Jack Klotz says:

    I have heard there is a process now to reverse the nuking, resulting in the glass being returned to its original state. Have you heard this as well, and if so, how does one do this?

    • David says:

      From what I have read or heard, whether any changes can even be effected, it will depend primarily on the glass formula/recipe. So many variables are at stake when glass is being made. In some cases a reversal, either partial, or nearly complete, might be accomplished by slow heating in an oven, or in some cases after several months of being left outside in ordinary sunlight. I don’t have enough solid information to elaborate further, and I can’t claim to be an expert on the subject of nuking. Perhaps someone more conversant with this will chime in with more feedback.

  5. Mary says:

    Thank you for the informative site! I collect sea glass and selenium can also create “sun yellow” pieces, which are pale or straw colored from exposure to sunshine.

    • Albert.K says:

      are artificially purpled artifacts more valuable than the normal colored one?

      • David says:

        That’s a matter of opinion, but in my view, no. Their authenticity as historical objects has been compromised by color alteration. There is a false perception by the average flea market shopper that they are worth more, but that is because of the prices of such items being asked by unscrupulous dealers, and the unknowing public who is willing to pay more for those items, having little or no background knowledge about those colors and how they were achieved.

  6. Fred Puttroff says:

    Here’s a current eBay auction with an altered Ball jar and my contact with the seller to which I received no reply. eBay Item No. 141152627582 I tried to be nice by saying that these can add to a collection; but they’re only a peculiarity and they are not worth what this jar is bringing.

    “Dear t****b,

    I would like to share with you that Ball never made this jar in Amber or Olive Green. This jar has been zapped or exposed to a strong radiation source(probably industrial in nature). This jar was made from 1923-1933 without the underscore. It was discovered, in times past, when jars were stored after use, upside down on fence posts, that the clear glass would turn amethyst over the years after exposure to UVA, UVB radiation from the sun. So, people whom have access to a radiation source expose numbers of clear jars hoping to hit the jackpot with purple/amethyst jars (they’re usually much darker); in that process some turned a type of amber color and they’re being sold as unique/rare Ball jars when that is not the case. I don’t think there’s any evidence that jars ever turned amber from sun exposure. It’s been reported that these zapped jars can lose the color when exposed to heat or microwave; but I don’t know if that is true. These can add to a collection.”

    • David says:

      Thanks Fred. These jars that are being “nuked” are a scourge on the glass-collecting hobby. It certainly confuses many newer collectors who are not sure about the history/authenticity of a particular piece.

  7. Pingback: From clear to purple or brown, that’s how irradiation runs | Peachridge Glass

    • David says:

      Thank you very much, Ken! Great article….. and yes, I should have explained in better detail that glass containing selenium (esp. common during the 1920s-1940s era) often has a faint yellowish, “straw” or “peach” color (for example, alot of the insulators made by Whitall Tatum during that time period) and so they may end up assuming that weird “burnt amber” or ugly dull brown color after being subjected to irradiation. ~David

      • Mary says:

        Does anyone know about Hemingray insulators? I have 2 that are a teal color it says made in U.S.A. It also has “No 20” on it.

        • David says:

          Mary, just google “Hemingray insulators” and you will come up with lots of websites about them. Try checking out and others. The “No 20” style is classed as a “CD 164” in the “CD” (Consolidated Design) system of identification used by insulator collectors. The Hemingray No 20 is a very common style.

Comments/Replies: All comments are moderated so will not be published immediately. Because of mail volume received, and time and energy restraints, some questions may not be answered individually, especially if the subject is already addressed elsewhere on this site. This website is not intended as an appraisal service, but as a resource for background info on glass companies and the marks they used, so I usually delete "What is this bottle worth?" types of queries. Thank you very much for your patience & understanding !!