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What Are Didymium Safety Glasses?

Didymium Bead Making Torch

Didymium Safety glasses have been known by many names including ACE, rose glass, rose didymium, ACE 202, Purple glass or Phillips 202.  There is no difference between them as they all refer to the same type of lenses.

Didymium glassworking lenses work to protect from Ultraviolet and sodium flare which are dangers relating to lampworking / torch work.

Sodium Flare occurs when a worker is using soft glass and borosilicate glass. Borosilicate glass also releases Infrared as well as Ultraviolet and sodium flare. If you find yourself using both types of glass, there is the option of using a green shade 2, 3 or 5 in a flip down style. This then clips onto your didymium glasses which will help protect your eyes.

If you are only using borosilicate or pyrex glass then our Green Ace lenses in a shade 3 or 5 would suit you best.

When choosing your didymium safety glasses you should know the below information:

  • Didymium glasses are also know as ACE, Phillips ACE 202, Purple Glass, Rose Glasses and Rose didymium.
  • This filter will protect your eyes from sodium flare and UV radiation when you are working with silver soldering, beadmaking or other soft glass work.
  • Didymium glasses cannot protect your eyes from Infrared radiation. This comes from borosilicate glasses or during kiln observation. If you are using this type of glass or viewing a kiln you should include a pair of flip down clip on’s in a green shade.
  • Didymium glasses are available in many types of frame styles including wrap around, standard and economy frames and are also available with prescription.
  • Although didymium lenses are traditionally made from glass they can also come in plastic and are known as Sodium Flare Polycarbonate (SFP) lenses.
  • If you are doing any sort of glass work with soft glass or silver soldering, then you should be using a pair of didymium glasses.

Should you not be sure about which type of glasses you should be using, get in touch. You can contact us for advice and guidance on purchasing a pair to ensure that you have the correct protection for the work you are doing.

We are hoping that we have answered your question for What Are Didymium Safety Glasses, but if not read on….

The History of Didymium

Didymium is a twin element and is a mixture of praseodymium and neodymium.  Didymium itself was first discovered in 1841 by Carl Mosander.  

It was not until 1874 that Per Teodor Cleve proved that Didymium was actually made up of two elements and not the three elements that had been previously thought.  However it was not until later in 1885 that Carl Auer von Welsbach was successful in separating the salts of the compensating elements praseodymium and neodymium.  

Over time the first syllable was dropped for both praseodymium (green didymium) and neodymium (new didymium). These days it is simply known as Didymium.  This is partly because of its use in glassblowing safety glasses and protection for blacksmiths.  The word is still used in mineralisation texts.

The Didymium filter is most frequently used with a gas powered forge, gas torch or soldering torches. In this situation it specifically blocks the yellow light . This wavelength is is emitted at 589nm by the sodium contained within the glass. Didymium or Rose Glass protects the eye from Visible and UV light which is a by product of the glassworking process.

The didymium filter is preferred as it retains a high VLT (visible light transmission). This means the worker can still retain sight of their work whilst wearing the glasses.  This is unlike some welding shades where nothing can be viewed through the higher shades without the addition of light.

This type of protection by using didymium was first discovered by Sir William Coates. Coates was a British chemist and physicist who attended the Royal College of Chemistry in the 19th century.

Use of Didymium in History

Didymium was used during World War 1 to transmit Morse code across the battlefields and ensure communications reached the right people.  Soldiers attached a prism to glasses which were then used to view the absorption bands switching on and off. This proved a vital tool in the success of armies and communications.

Use of Didymium Today

This staple of the glassworking industry, Didymium Safety Glasses, ACE Lenses and Phillips 202 lenses have been used for many hot glass applications such as furnaces, kilns and torches. It is known for being dichromic. This means that it shows different colours when exposed to different light sources. For example under white or glowing light the lens will retain its rose colour. Under fluorescent light it will become green / blue.

There have been many experiments carried out with Didymium filters over the last few centuries.  The spectral analysis of this filter shows that it provides good protection from UV light up to 360nm. It also provides excellent protection against sodium flare and excellent overall visible transmission from 400 nm to 725 nm. 

It is worth bearing in mind that Didymium does not block light from the infrared range. So it is not suitable for use for any glassworking application that may cause the emitting of this light range.

There are several applications where this filter would be the preferred option.  These include beginner glassworking using hot head torches (MAPP gas). If soft glass is being used it would be suitable for propane gas torches.  Kilns and furnaces should only be viewed with didymium glasses for short viewing periods. These tend to emit infrared for which this filter is not suitable.  Didymium is also suitable for a range of acetylene torch work, gold jewellery and enamelling of jewellery.

The didymium filter is not to be used for lengthy periods of time for work with temperatures exceeding 1000 degrees. It is also not suitable for use with hard materials such as borosilicate which would require high pressure torches to be used.

What Are Didymium Safety Glasses? – Phillips 202, ACE, Didymium Lenses

The Phillips 202 filter that is used within Safety Protection Glasses’ Didymium glasses uses rare earth oxides within its composition. This is also known as ACE, short for “Amethyst Contrast Enhancer.”

This contrast enhancer works by selectively positions the transmission of red, blue and green spectrums. This helps to improve the colour discrimination allowing for different colours to be viewed through it.

The ACE filter effectively filters the sodium flare and prevents ultraviolet light up to 390nm.  The Didymium filter also provides a VLT of around 38%, and so is the preferred choice of glassworkers around the world.

Do you need more information on what type of glassworking glasses you need? Find more information in our next article Which Safety Glasses Should I Use For Glassworking?



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