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TECHNICAL INFO - ALUMINATES

PRODUCTS

1. What products does Artemis sell?
Our standard line includes 5 types of powdered pigments:

Glow in the Dark Aluminates
UV Reactives
Glitters
Thermochromes
Up Converters (also called Anti-Stokes)

We like to say that we are experts in “photoluminescent specialty pigments.” Technically, these aren’t all photoluminscent pigments, but they do all deal with changing colors and altering wavelengths of light in some manner, so close enough.

2. What are the most common applications for Artemis pigments?
Paints, inks and plastics made using our pigments are commonly used in a very wide variety of applications (see our Applications document for a very long list), but generally:

Glow in the darks go into safety signs, tape and other markings
UV Reactives and Up Converters are used for anti-forgery markings
Glitter and Thermochromes are used in decorative and novelty items

3. How should I choose among the various Artemis pigments?
With glow in the darks (GID’s), go for the largest particle size you can handle in your application because that will give the brightest afterglow. Other than that, it’s just a matter of choosing the pigment with the body color and afterglow color that you want for your application.

With UV reactives, go for the organics if you they will work in your application because they are generally brighter. However, they are also less stable. So, for example, they would be good for a consumable like shampoo and bad for an outdoor paint that’s meant to last 10 years. In any event, it’s usually worth doing a quick test on both the organic and inorganic version of your chosen color(s).

4. How do Artemis pigments work? What is photoluminescence?
Most pigments just (i) absorb certain light wavelengths and (ii) reflect others, but our fluorescent and phosphorescent pigments also (iii) absorb certain wavelengths and re-emit that light energy at different wavelengths. That is, they use energy from the photons in lightwaves to achieve a glow or “luminescence.” Thus, they are “photoluminescent.” Normal pigments are “passive.” Because of (iii) above, our pigments are considered “active.”

Because there are many ways besides photons of getting energy into a pigment, there are many types of luminescent (i.e. light emitting) pigments. For example, the pigments on TV screens get their energy from fast electron bombardment - “cathodoluminescence.” Radioactive pigments get their energy from internal atomic decay - “radioluminescence.” Other pigments get their energy from heat - “thermoluminescence,” and still others from frictional forces - “triboluminescence.”

Luminescence can be split into “fluorescence” and “phosphorescence,” which define the absorption/emission process. Fluorescence happens virtually instantaneously, so you see no afterglow, whereas with phosphorescence there's usually a delay, so you get an afterglow. Not always, but that's a good guide.

For example, a typical daylight fluorescent orange will (i) reflect orange, (ii) absorb red and yellow and lose it internally, and (iii) absorb green and blue and re-emit this energy as orange light. So you end up with much more orange at the end of the process than you had at the beginning, up to four times more. That's why daylight fluorescent pigments look unnaturally bright. These are called “daylight fluorescents” because they absorb and emit in the visible spectrum, but there are other fluorescents. For example, our UV reactive pigments are fluors that absorb in the UV range and emit in the visible range. Our phosphors absorb blue and green visible light, hold on to it for a while, then re-emit it. “Pure” pigments have emissions confined within a narrow emission band. Dirty pigments produce “dirty colors” with wider emission bands, and/or several emission bands.

Here are some excellent articles on photoluminescence and applications:

5. What special items does Artemis make that aren’t on the product list?
We’ve also done literally hundreds of special order pigments, so don’t hesitate to ask. Here are some examples:

Smaller particle size phosphors
Phosphors that glow white
Phosphors with a pure red afterglow
UV reactives that are invisible under regular, long UV but glow under short UV
Phosphors with specific emissions at particular wavelengths for computer recognition in security applications

6. What products does Artemis have on the drawing board?
In the coming months we will be adding daylight fluorescents. We are also looking into bacteriorhodopsin and flop colors.

7. Are Artemis pigments safe?
Yes. Our pigments are free of heavy metals and are not radioactive. They have no known harmful effects to people or the environment. However, they have not been declared safe for human consumption by the FDA and therefore should not be ingested. Please read the Manufacturer Safety Data Sheet provided with the product for complete information.

As with any powdered chemical, standard safety precautions apply: Direct contact may cause irritation of eyes, nasal passages, throat, and skin. If such irritation occurs, wash the affected area with clean water. Keep the products sealed in a container and free from moisture when not in use. When handling our products you should take standard precautions such as wearing gloves, goggles, dust mask and other appropriate safety devices.

8. How long will Artemis glow in the dark pigments work? When will they degrade?
Our aluminates will charge up and glow repeatedly for at least 10 years, and possibly much longer depending on the conditions. Generally, it is more important to choose a tough, long-lasting base paint or ink because our glow in the darks will usually outlast whatever they are dissolved into. They are also capable of surviving very tough applications. For example, one of our military customers uses them in artillery to identify each bomb after it has exploded.

9. How long will they glow?
Because the brightness and length of afterglow varies depending on many factors, we make no express or implied warranty as to those characteristics of our glow in the dark pigments. Please test them yourself in the environment in which they will be used.

COATINGS APPLICATIONS

10. How much pigment powder should I use?
There is no simple answer to this question. It depends upon many factors: the brightness desired, the method of applying the coating, the amount you want to spend on the item, etc. The brighter you want the coating to be, the more pigment you must mix into it, but then the more expensive it becomes. You must experiment to find the right mixture for your particular application.

A typical range might be 5% to 50% by weight. Under 10% may look grainy, especially with pigments having larger particle sizes. Over 50%, the coating may start to get brittle and flake off. The coatings on safety signs are often around 50%, but some have been known to push the ratio north of 70% to get as bright a glow as possible.

11. What is a good “recipe” to use as a starting point for mixing glow in the dark paint?
If the supplier of the base paint offers a starting formulation, use that. Otherwise, a typical mixture might be: 25% pigment, 20% calcium carbonate as filler, 55% clear base paint. All %’s are %’s of the weight, not the volume, of the final mixture. You may sometimes see a reference to a P:B ratio. This means Pigment to Binder, and it is just another way of describing a mixture. P:B ratios are always to binder without any additives or thinners.

Like the amount of pigment used, the amount of filler used can vary dramatically. Filler is important because it is cheap and brings down the cost of the finished product. It can also help prevent settling of the pigment and give a thicker consistency to the paint or ink. There are two common types of paint filler that are translucent enough to be mixed with photoluminescent pigments without quenching their photoluminescent properties:
1. Calcium Carbonate - CaCO3 is heavy, so up to 30% by weight is normal. You can usually just use the cheapest CaCO3 you can find.
2. Fumed Silica - Because it's light and fluffy, a few percent by weight is big volume and should be enough. Aerosil 200 from Degussa works well.

Keep these things in mind:

Use the clearest base coating you can find. DO NOT mix our pigments into a tinted paint, ink or dye or any other opacifier. Anything that is not clear and translucent will quench the photoluminescent effect of our products.
In paints, completely clear non-yellow lacquers are best, particularly acrylics. Clear enamels and urethane lacquers also work well. MinWax’s Polycrylic product is a good choice.
Do not use UV filters with any of our products.
Do not use acidic base coatings.
You can mix various colors of our pigments to design your own color.

12. How should Artemis pigments be used / applied?

To mix in our pigments, just throw them in and stir it all up using high speed stirring. Do not mill or grind.
Apply the coating over a white undercoat to reflect the inward bound luminescence.
Our pigments will disperse but not dissolve. If settling occurs, mix well just before use, and consider adding filler or an anti-settling agent.
For test batches where you only have a small sample of our pigment on hand, it works best to start with a fixed amount of pigment and slowly mix in the clear base paint until you get to the desired concentration. If you go the other way and mix the pigment into the clear base paint, you may run out of pigment and have to wait several days to get more.
Avoid any moisture in the mixture. Water may turn resins yellow.
Applying a clear overcoat will protect and extend the life of the glow coating.
Plastic stirring rods are preferred. Metal rods may react with the pigment powder.
You may need to apply several coats to get your desired brightness.
There is no substitute for doing a small test of the coating in the environment in which it will be used BEFORE proceeding with the full application. It is an absolute must.
Apply the finished coating as you normally would. For example, if it is a paint, use a brush, roller, or sprayer, etc.

13. For the glow in the dark pigments, should the coating be solvent or water based?
All of our aluminates work in solvent based systems. However, our green aluminates (SA-1/9/12) will not be stable in water based formulations, so you must use SA-5. Because it works in water based paint, SA-5 is popular in places where solvent based paints are illegal for indoor use due to the fumes. A good water based acrylic is Texicryl 13-031 from Scott-Bader. It’s very clear and cures hard. Water reducible Polyvinyl Acrylics (PVA’s) are also good.

14. What are some examples of solvent based paints and applications?
Epoxies - floor paints
Polyesters - good for outdoor use because tough
Nitrocellulose - car refinishing, golf balls
Vinyls - huge variety of applications
Note: Acrylics come in both water-based and solvent-based versions.

15. Can Artemis glow in the darks be used in auto paint?
Yes. In fact, we have a truck that is painted with our glow in the dark pigments. It was done by a refinisher in London. He just took 5 kilos of SA-1 and stirred it into his lacquer, then sprayed it on. That gave a matte finish, so he gave it a couple of coats of overlacquer. Looks fantastic and has a white body color so it just looks like a regular, white Nissan Patrol until the sun goes down. The pigment has been on three years, parked outdoors, and has not degraded at all.

16. Do Artemis pigments work well on porous surfaces? Non-porous surfaces?
Yes, but this is more a function of the paint or ink than the pigment.

PRINTING APPLICATIONS

17. Does particle size make a difference?
Yes. Finer particle size is generally better for screen printing and flexographic printing, as explained below. Of course, with glow in the darks you always want to choose the largest particle size that you can handle for your application because larger particle size = brighter glow.

18. Will Artemis pigments work with UV cured inks?
Yes. Our pigments can just be mixed into the UV curing ink. However, pigments don’t dissolve into UV curing inks, so there are two ways to prevent the pigment from separating from the ink:

1 - Match the specific gravity of the ink to the specific gravity of the pigment, or
2 - Adjust the rheology (flow) of the ink by adding something like fumed silica (very pure finely divided sand) such as Aerosil 200 from Degussa. Fumed silica is a very light, fluffy, white translucent powder which doesn't affect the luminescence. This makes the formulation more gel like, giving what formulators call “structure” to the ink, which gives better image quality.

Note: particle size doesn’t matter one way or the other in the UV curing process. However, most UV cured inks are screen printed, and in general smaller particle size is better for screen printing. See the question on screen printing below for more info.

For those who aren’t familiar with UV cured inks, the way it works is that the liquid polymer base of the ink is crosslinked (i.e. cured) by short wave (“hard”) ultraviolet radiation. This takes about a fifth of a second, so you can print something, pass it under high intensity short UV lamps at high speed and it comes out bone dry at the other end. The UV source must be well contained because short wave UV is dangerous. In their unpigmented state the liquid polymers that compose UV curing ink look rather milky. The liquid polymer is made into an ink by adding solids (pigments, fillers, additives, etc.). On exposure to short UV it almost instantly becomes solid, much like molten glass solidifying on cooling. Nothing boils away. It just changes from liquid to solid.

19. Will Artemis pigments work with flexographic inks?
Yes, but only with our custom products that have 5 micron particle size. Flexo inks are usually colored using soluble toners rather than insoluble powdered pigments like ours, but you can get away with small powder particles of about 5 microns. Larger pigment particles would mean a thick ink film, which would smudge. Also, big particles make the ink flow badly and therefore cause poor transfer off the raised surfaces to the substrate.

For those who aren’t familiar with flexo inks, they are applied using a steel roller with a rubber sleeve onto which the image is carved, i.e. a cylindrical stamp. Common applications are supermarket plastic shopping bags and cheap plastic containers. The inks have to be very thin, otherwise they smudge when the raised rubber surface comes into contact with the substrate. You can tell a flexo print by a “halo” around the print area. This is caused by the deformation of the rubber during printing.

For the previous 50 years flexo was all solvent based but, after a shaky start, water based flexo ink has become doable in the last 10 years or so. These water based flexo inks are heavily used in areas with strict emissions controls like California, and now it's reasonably popular, though they'll never be as good as solvent based inks. On the other hand, water based inks have the advantage of sitting where you put them, i.e. they don't spread out so much. This is because they don't like most substrates, whereas solvents will sink into every space between every fibre. This is because of low surface tension (as opposed to water’s very high surface tension). Water is difficult to disperse any solids into because the molecules of most materials used in the coatings business have edges or surfaces that don't like water. So ink makers use special dispersing agents, which usually work by having molecules that are hydrophobic at one end but hydrophilic at the other end. Tammol from BASF is an excellent one.

20. Can you screen print with Artemis pigments?
Yes. This is a very common application for our pigments. To make screen ink, buy a low viscosity, high transparency varnish, and just stir in our pigment. Do not mill or grind the pigment in as this will destroy it. It's always better to do one pass at high concentration (say, 50% pigment by weight) than several at lower concentration.

Choosing the correct mesh for the screen is tricky. Finer mesh allows the printer to put down a thinner film, which will be cheaper and will produce finer detail, whereas coarser mesh allows you to use larger particle sized pigment and to lay down a thicker layer of ink, both of which lead to a brighter glow. A 100 mesh is a good starting point, but you can go higher or lower. A good range might be, say, 80 to 120. In any event, stay below 200. Ulano is one good mesh producer that we have seen used successfully with our pigments.

You must use a good opaque white base coat of the same polymer system as the varnish. Trying to save a few cents by using an inferior translucent white undercoat will end up costing you more in lost performance. This may have to be a flame retardant type if you're printing on to plastic or fabric.

Over the top it's best to apply a clear non-yellowing overlacquer, again of the same polymer system as the varnish. This is purely for physical protection as the phosphor coating will be very matte and will be easily scuffed. UV protection is not necessary as aluminates will last many years. The carrier systems will degrade before the pigments. One last note, phosphorescent printing of signs, etc. is usually done whole sheets at a time using flood coating.

SAFETY SIGNAGE APPLICATIONS

21. Can Artemis pigments be used in safety signs?
Absolutely. This is a huge business and is the “bread and butter” of the photoluminescent pigments industry.

22. What are the standards for safety signs?
In the United States, there are many standards on the use of photoluminescent materials. To generalize wildly, more or less all such standards are in the process of being upgraded to require aluminate glow in the dark pigments rather than sulphides. That is why selling glow in the dark pigments to manufacturers of safety signs, tape, markings, etc. is very good business. Here are some of the many standards that require the use of photoluminescent materials for safety purposes:

State building codes
Many states’ building codes require photoluminescent safety signage and specify in great detail how bright the products must glow, where they must be placed, etc. California, Washington, Illinois, Florida, New York, Wisconsin, and Oregon all have extensive requirements. In Canada, Ontario, Alberta, and Manitoba have similar requirements.

Ships
Photoluminescent products are widely used in the maritime industries. The 1974 Safety of Life At Sea (SOLAS) Convention governs international shipping, and it has adopted International Maritime Organization (IMO) Resolution A752 (18), Guidelines for the Evaluation, Testing and Application of Low-Location Lighting on Passenger Ships, which requires "low-location lighting" (that is, photoluminescent marker strips) on all ships carrying more than 36 passengers.

Another standard is the International Organization for Standardization ISO/CD 15370, "Ships and Marine Technology - Low-location Lighting on Passenger Ships - Arrangement." This document is intended as a supplement to IMO Resolution A752 (18). The American Bureau of Shipping (ABS) reportedly intends to use ISO/CD 15370 as an approved test guideline for their ABS Product Type Approval.

Aviation
The US Department of Transportation Federal Aviation Administration Advisory Circular 25-812.2 "provides guidance material for use in demonstrating compliance with the provisions of Part 25 of the Federal Aviation Regulations (FAR) regarding floor proximity emergency escape path marking systems (FPEEPMS) which incorporate photoluminescent elements." This document is not mandatory, but rather provides guidance for aircraft manufacturers in demonstrating compliance with the safety standards set forth in the rule. Interestingly, zinc sulphide materials are specifically excluded from use. Only strontium aluminate materials are acceptable, although newer materials providing equal or superior performance "may be considered."

The discussion above borrows heavily from this source: http://www.duracorp.com/Articles/GlowAndBehold.htm
To give you a feel, here is a typical standard:
http://www.pspa.org.uk/standard/standard1/page10.html

23. Will all Artemis aluminates work for all safety signs?
No. It depends on the standard you must meet. In sufficient concentration, most of our regular, uncolored aluminates will meet the high bar on most standards. However, our red SA-30 and SA- 40 cascaded pigments are mainly for novelty applications, and they are unlikely to be suitable for escape systems. The bottom line is that customers must confirm for themselves whether a particular pigment will meet a particular standard.

24. Can Artemis pigments be used in reflective road signs?
Yes. The very bright signs you see on road sides use “retroreflective” technology pioneered by 3M many years ago. The patent has lapsed now, so there are lots of manufacturers making them. Any of those manufacturers might be interested in adding glow in the dark or daylight fluorescent pigments to their signs. We have GID’s today, and we will be adding daylight fluors to our products list in the coming months. Note that creating retro-reflective signs requires the use of heat welded plastic films which we do not supply but which are readily available.

In case you are unfamiliar, retroreflection is a method of turning incoming light around and reflecting it straight back toward its source. It is done using (i) a shape, such as a three dimensional pyramid, that bounces light straight back at its source, and (ii) “internal reflection” rather than traditional silvered mirrors.

To understand the way a three dimensional pyramid (“tetrahedral”) shape retroreflects light back directly towards the source of the light, consider looking at three mirrors, all at right angles to each other, say on the two walls and the ceiling. Now, wherever you stand in the room you will see yourself straight ahead. A light beam sent into the corner at any angle will bounce three times and come back out parallel to the direction it went in. Two other shapes that retroreflect are spherical and hexagonal.

To understand “internal reflection,” consider the way a stick appears to “bend” when it is immersed in water. The reason is that when light passes from a more dense transparent medium to a less dense one, if it hits the surface at a slight angle it will be bent. This is caused by the differing speeds of light in those media. The degree of difference is called the “refractive index.” At large enough incident angles where there is a large enough refractive index, light will not pass through the interface, but will bounce back. This “internal reflection” is 100% efficient. Unlike reflection from a conventionally silvered mirror, nothing is lost.

There are two common commercial methods of achieving the retroreflective effect on signs: (i) plastic sheets with tetrahedral or hexagonal shapes printed into them using heat (explained below) and (ii) Ballotini beads. In both cases, a 3 layer system is used: (1) a white base, (2) a layer of pigmented paint or film which may contain daylight fluorescent pigments and/or glow in the dark pigments, and (3) a layer of some translucent substance such as plastic or lacquer containing either tetrahedral/hexagonal shapes or Ballotini beads.

Ballotini is harder to use and is not as efficient, but you will have to use Ballotini if you are restricted to paints, or if you are coating a surface that gets hot during use, such as the exhaust pipe of a motorcycle. Here is more info on Ballotini beads: http://www.pottersbeads.com/markets/highwaysafetystandard.asp

Plastic sheets containing tetrahedral shapes are made as follows. One plastic sheet is heated and run over a hot metal roller that has lots of little regular pyramids sticking up. That sheet is allowed to cool and harden. It is then placed on top of a softer plastic sheet and together they are squashed through a pair of heated rollers (called a “calender”) so that they fuse together. Here is a link to more info on retroreflectivity: http://www.3m.com/intl/AU/reflective/

OTHER APPLICATIONS

25. Can Artemis pigments be used in plastics?
Yes. Our pigments can be used in any plastics technique: blow molding, casting, extruding, coating, injecting, and dipping. As an example, the method of use of our pigments in plastic extruding is as follows. The dry pigment goes in the hopper with all the other components at the beginning where it all gets mixed up by the rotating blade. Then the mix gets drawn into the extruder which melts the plastic pellets and mashes everything else into the plastic. This produces a gooey tube of colored molten plastic which goes into a mould.

26. Does the hardness of strontium aluminates pose any risks to machinery?
Yes. When mixing our strontium aluminate pigments into polycarbonate, keep in mind that the granules are very hard, so the client will need to use a lubricant in his plastic processing equipment (extruders and moulders, etc.) otherwise he'll (a) purge all the muck stuck to the insides, then (b) start abrading the steel linings. Either way the nice clean extrudate will turn dirty grey after about two minutes running. A typical lubricant is micronised wax, but every plastics processor has his own favorite that he knows works in his equipment.

27. Can Artemis aluminates be used in molten glass or other very hot applications?
Our pigments are fired at about 1250 C, which is about 2280 F. So they should not be used in any application that will be hotter than approximately 2000 F. As always, it is critical to do a test run.

28. Can Artemis pigments be used in cosmetics?
Yes. The SA’s and UV’s will all work. The organic UV’s are preferred because they are brighter than the inorganic UV’s. The organic UV’s are a bit less stable, but that shouldn't matter for a consumable like shampoo or other cosmetics. Boots, one of the largest drugstore chains in the UK and Germany, uses our pigments to create a line of “Disco” cosmetics such as nail polish, lipsticks, mascara, etc.

29. Can Artemis glow in the dark pigments be used on candles?
Yes. It works best when the pigments are in a clear coat on the outside of the candles. Start with a finished white candle, and dip it into highly pigmented molten wax. If you put pigments into the body of a candle (i) the flame goes out, and (ii) you dont see the effect anyway. You may have to dip the candle several times, drying between dips, to get the desired effect.

30. Are Artemis pigments edible? Can they be used in food?
No. As far as we are aware, no luminescent dye or pigment, fluorescent or phosphorescent, has FDA approval, and is ever likely to have because nobody's prepared to pay the $100,000 or so for the trials. Consequently, we can't recommend our products for any application that involves the product entering the body. This includes food, tatooing, etc.

Mick’s opinion is that aluminates probably wouldn't do harm in the gastro-intestinal tract. Sulphides, on the other hand, would react with stomach acid forming hydrogen sulphide. Most fluorescent pigments have free formaldehyde, so they'd be a problem in the stomach too. However, if the pigments are encapsulated in a thermoset carrier, e.g. dried crosslinked paint, then you'd be dealing with the chemistry of the dried paint rather than that of the pigment.

Mick has worked in the industry for decades and has never heard of any factory worker suffering any ill effects from contact with luminescent pigments. Also, we once had some pigments tested by a German company to determine if they would be safe for fish, and their conclusion was that it would be safe.

31. Will Artemis glow in the dark pigments react with chlorine? Can they be used in swimmig pool equipment?
They will not react with chlorine. They are safe for use in swimming pool equipment.

32. Can Artemis pigments be used to make markers and pens with UV reactive ink?
Yes. Just buy fiber tipped pen cases and fill them with UV organic pigments dissolved in alcohol. Don't use the inorganic UV’s because they will block the tips.

33. What are some applications for Up Converters?
Up-converters are very obscure and used entirely for anti-forgery applications. When fired up with an infrared laser they glow different colors. They are currently in vogue for cutting edge anti-forgery applications because if the forgers don’t have an infrared laser, they won’t even know the Up Converting pigment is there.

These are also called Anti-Stokes pigments because they violate the standard Stokes emission process by absorbing infrared light and emitting higher energy / shorter wavelength visible light. In other words, these pigments emit higher on the electromagnetic spectrum than they absorb.
http://www.cheniere.org/misc/antistokes.htm

Several years ago Mick gave a talk at the University of Manchester Institute of Science and Technology on anti-Stokes luminescence and someone from the Bank of England approached him afterwards to give him an ear bending for giving secrets away. These pigments are still pretty sensitive, so don’t give out samples and/or sell to anyone that you think might be a forger.

34. What are some applications for Thermochromes?
There are many novelty applications. And for anti-forgery, you can hide a UV and a UC image behind a TC covering. To find all the traps, the forger has to warm the TC pigment and quickly shine UV light and an IR laser on the underlying area.

35. Can our products be combined for anti-forgery applications?
Yes. They usually are. For example, we have a custom order product which is a short UV Red, YOS.Eu, which emits bright red under short UV but nothing under long UV. If a security ink maker were to combine this red with a long UV emitting pigment, he'd have an ink that is one color under short UV and a different color under long UV. Suppose then he added an afterglow phosphor, that would make it yet a third color when viewed in the dark. Then when you start mixing in up converters and thermochromes, you can make forgers’ lives very difficult.

TECHNICAL INFO - ALUMINATES

36. How do strontium aluminate glow in the dark pigments compare with sulphides?
The old GID pigments were made with zinc sulphide. They degrade quickly, have short afterglows and sell for much less than aluminate GID’s. Today, zinc sulphide GID’s are used mainly for novelties.

Strontium sulphide (SrS.Eu) has a similar performance to zinc sulphide, i.e. the glow goes in about an hour. And it gives off an odor because it releases hydrogen sulphide. As a result, it must bear a warning label that “contact with acids liberates toxic gas.” All sulphides have to carry this warning, but SrS is the worst of them.

There is another sulphide GID formulation also. Calcium strontium sulphide is slightly less smelly but not as bright and not as nice an afterglow color.

37. Are there any standard tests for measuring brightness, length of afterglow, etc.? What is DIN67510?
DIN67510 is the testing system we use to measure afterglow materials.
DIN results are expressed in the form a/b-c-d-e, where
a is brightness after 10 minutes
b is brightness after 60 minutes
c is the time in minutes to extinction (actually defined as time to 0.32mcd/m2, which is about ten times the absolute limit of human perception)
d is a code letter for the absorption color
e is a code letter for the emission color

DIN is the German standards institute. They will evaluate a sample for you, but it will cost almost $2000. Artemis is one of the few organizations in the world that is approved by the PSPA (http://www.pspa.org.uk) to perform the DIN67510 test.

38. I saw incredible glow times advertised somewhere. Are they accurate?
Probably not. The only valid way to compare the performance of pigments is to use a standardized test. For glow in the darks, the most common test is called DIN67510 (see question on DIN67510 for more info). If anyone claims DIN67510 numbers higher than ours, they are probably lying. However, rather than arguing about it, it’s best to just give the client a sample and let them compare the products in their own environment.

There are many ways to get inaccurate glow time numbers: charge up the pigments with high energy UV light instead of visible light, measure the time to extinction in a room with another light source (which will slowly recharge the pigment as it is emitting), charge the pigments for more than the 5 minutes at 1000 lux stipulated by all standard tests, etc.

Also, “self-emitting” pigments will have longer glow times, but that’s because they are radioactive. You probably will never run across anyone selling these. They are out of favor for obvious reasons.

39. How do you make colored versions of the basic SA products? What are cascades?
Our SA-20/30/40/50 phosphors are all cascades (i.e. “blends”). All of our cascaded phosphors are green emitting (except SA-50 which is based on SA-5 and thus blue emitting), and we take the green emission and shove it up, or down, the spectrum. Anything close to green, such as yellow, is easy to cascade, anything further away, such as red which is at the bottom of the visible light range, is much more difficult. The trick is to get the emission curve of one luminophor to coincide with the absorption curve of another, but it never quite matches, and the further you cascade, the more energy you lose (i.e. “quantum yield” is low).

All these cascades have pastel body colours, quite deliberately. And they all emit in a fairly broad range of visible light. If you want a purer, narrow band, blue emitter, SA-5 is perfect. If you want a pure red emitter, we do two custom materials, one white bodied (an aluminate), one dirty pink (strontium sulphide with europium, has a sulphur odor). Pure red afterglows are never as intense or long lasting as greens and blues. We get them better every year, but as fast as we improve the reds, the greens (with the same improvements) are improved even more.

40. Can the body colors of the SA pigments be 'darkened'? Must they be white or pastel?
Body colours will only ever be white or pastel. Strong, dark body colours, by definition, mean strong absorption right across the spectrum, with narrow reflection bands. That's a conventional pigment. No good for phosphors. Kills luminescence stone dead. Light has to get in and out again.

41. What is an absorbtion/excitation/emission spectrum? How is this expressed as a curve?
The absoption or excitation spectrum (same thing) tells you what wavelengths of light are going into a fluor or phosphor and being absorbed. The emission spectrum tells you what wavelenghts of light are coming out and being emitted, i.e. what color(s) it fluoresces or phosphoresces.

The convention for illustrating absorption/excitation/emission spectrum graphically is to plot a dotted curve, which is usually bell shaped, on a graph. Intensity is measured up the side, and wavelength is measured along the bottom. The absorption and emission spectra are usually plotted on the same graph and often overlap slightly. The taller the bells, the more intense the absorption/emission. The narrower the bells the purer the color.

42. Can a phosphor emit only at one particular wavelength?
Emission colors can be made purer, but generally the narrower the emission band the dimmer the emission. We have phosphors with specific emissions at particular wavelengths for computer recognition in security applications, most made exclusively for a single customer to identify a product.

43. Can phosphors ever be completely clear?
No. All afterglow phosphors for coatings and plastics are opaque inorganic solids. So the best you'll get is white. There are a few translucent organic afterglow materials, water based naphthalin derivatives mainly, but they're only used in microbiology for labelling specimens and fizzle out quite quickly. These are no good for coatings. There are also chemiluminescent materials which are very bright for three or four hours after two clear liquids mix, but then they fade away. Both of these would not be usable in typical coatings for health and safety reasons.