For some time now, there has been a product called ‘Didymium II’ floating around the industry. It is manufactured by Oberon out of New Bedford MA. It is cheap, only $24.00 retail, but, what exactly is ‘Didymium II’? Is it some new-fangled invention or combination of elements no one has ever heard of?

No. ‘Didymium II’ has no didymium in the formulation of the lens. It is simply a dyed polycarbonate lens with a gold coating. Take a look at the attached transmission chart of ‘Didymium II’ (chart 1), showing visible light transmission between 200 nm and 1000 nm. Compare it to TRUE didymium (chart 2). TRUE Didymium is a combination of neodymium and praseodymium, which are rare earths that create the classic didymium transmission spectra.

First note that the average visible light transmission of ‘Didymium II’ is only 10 %. This means that 90% of visible light is being blocked by this lens. The darkest commercial sunglass transmits an average of 20%, or blocking 80%. This lens is manufactured by Schott Glass Technologies, and is referred to as Grey 3 or S-4020. Standard thickness is 2.2 mm. ‘Didymium II’ is a very dark lens. To safely use this lens, you need to be either working outdoors, have an extremely well lit studio (with something like flood lights!), or remove the glasses when you move about your studio. Compare this to TRUE didymium, which has an average visible light transmission of about 50%.

Then, note the sodium area between 575 nm and 600 nm. Note that TRUE didymium has a very narrow notch (or filtration) in this area. Compare this to ‘Didymium II’, which has a very wide notch from about 525 nm to almost 700 nm. This means that not only is the yellow being cut out, but a good chunk of green, orange, and a lot of red. Since this lens is so dark, it is almost impossible to see any kind of color definition, especially as your glass is heating up.

Additionally, polycarbonate lenses are susceptible to scratching. If your studio has any glass chips floating around (what studio doesn’t?), and one of those chips is wiped across the lens, you will have a scratch immediately. If you have a habit of placing your glasses lens down, this will significantly increase the risk of scratching or wearing the coated surface of the lens.

Oberon (and others) take great pains to tout the ‘Gold Coating’, some even comparing it to the coating that NASA uses on the astronaut visors. But what they don’t say, is that the gold coating on the astronaut visor is only the TOP coating. The quality of the coating that Oberon uses cannot even begin to compare to that of NASA’s.

So, what does the gold coating actually do? It does reduce IR, but most of its attenuation is in the visible light range. It acts as a visible light reflector, reflecting (and preventing transmission) of visible light. So what does that mean? It means that not much light gets past the coating (and according to the transmission chart, in combination with the dye, only one photon in ten makes it through to your eye).

TRUE didymium does transmit IR radiation. We do not deny this. But is it a risk to you? That depends on the work that you are doing. What type of glass you are working, the torch and gas combination you use, and how close you work to the torch all affect the amount of IR that you are exposed to.

For example: if you are working soft glass making small beads (under 2 inches) with a hot head torch and working less than 3 hours per day, your IR exposure is less than two hours in direct sunlight. But, on the other hand, if you are working borosilicate and using a major burner and oxy-propane or other high pressure mixture, your exposure is quite high and ordinary TRUE didymium will not provide either the proper sodium filtration, or IR protection.

Another example: if you are doing traditional glassblowing and working at a glory hole and/or furnace, you are being exposed to tremendous amounts of IR and you need to take steps to limit your exposure.

It is our belief that calling this dyed polycarbonate lens ‘Didymium II’ is at best misleading, and at worst, false advertising. It serves only to confuse people and has the potential to cause serious injury due to the darkness of the lens.

If you agree and wish to do something about this, contact the following Federal Agency and complain:

Federal Trade Commission

www.ftc.gov

This web site has directions and forms for filing complaints.

We challenge Oberon to either change the name of their product, or put obvious notices on their product descriptions stating that the product does NOT contain didymium. These notices should also be required by all re-sellers of the Oberon product.

Copyright © 2009-2010 Aura Visual Concepts, Inc., Sauk Rapids, MN 56379

Date of last update:1/19/2010