• Ultraviolet Photography
  •  

Question for Spectralon owners - cleaning?

31 replies to this topic

#1 JMC

    Member

  • Members
  • 148 posts
  • Location: UK

Posted 23 November 2017 - 20:48

Ok, this could be a great thing or a ridiculous purchase. I just put in an offer and won a set of 8 Spectralon diffuse reflectance standards from Labsphere on a well known online auction site. 2 of the standards are described as having "visible marks, roughly 1". These are likely removable, as standards are also fully washable per the manufacturer's website (see instructions)". I see this as a bit of a risk, hence I put in a low offer which to be honest I was surprised was accepted.

So, for those that have these things, how easy are they to clean, and what should I not do - scrub too hard, leave to soak, etc, etc?

#2 Andrea B.

    Desert Dancer

  • Owner-Administrator
  • 5,266 posts
  • Location: USA

Posted 24 November 2017 - 00:37

Dust, dirt and lint can be rinsed off Spectralon standards. They are very hydrophobic. I pat them gently dry with a microfiber cloth and let them stand for awhile before putting the lid back on. The purists amongst us would use distilled water for rinsing Spectralon. I admit to using my local tap water once or twice, so don't tell Labsphere, please.

All the Spectralon I have is rather easily scratched. Minor scratches and nicks can be sanded under running water. I usually just wet the sandpaper, put it on a table, flip the Labsphere disk face down on it and gently rub across the sandpaper. Of course, not all scratches and nicks will be completely removable depending on their depth. A deep gouge could affect the reflectivity and susequent use of a white balance tool because a deep gouge will photograph darker.

I use a much finer sandpaper grit than is recommended by Labsphere. I'll go look it up and get back to you on that. Also be sure that your sandpaper is not dyed in any way. I had some kind of reddish sandpaper once which seemed to release reddish dye when used wet. Not good for Spectralon. :D

Another potential problem with Spectralon is that it can become contaminated with hand oils or other organic substances or chemicals which may not be removeable. So don't touch the Spectralon directly with fingers/hands. Try not to spash coffee or beer on it. And so forth.

A couple of years ago my Spectralon rectangle (5"x5") got swiped by a ballpoint pen when I was out working, making notes and trying to swat away various little insect annoyances. I did manage to remove the ballpoint ink by careful sanding, but you can still see the indentation from the ballpoint. I think I was upset for about a year about that ballpoint incident !! But you know.....if you have tools, then you must use them and when using them, well, sometimes stuff happens. So I finally let the distress go. :lol: B)

It is my impression that the darker grey standards are more easily contaminated than the white and light grey standards? The darker ones may be a bit more porous??? (Not sure.) The black standard does seem ever so slightly grittier. Labsphere does recommend NOT sanding the black one.

One of my dark grey standards has begun to look spotty and may have to be retired. I don't recall what is added to make the grey standards or how that colourant might affect them. I should pick up the phone and ask Labsphere about it. They bear no blame for the spotty grey one because my using these standards "in the field" like I have done for the last 5 years is very hard on them. Pollen is a very sticky contaminating substance on both sensors and standards! Generally I'm pleased that my Spectralon items are holding up so well.

Hope this is useful.
Andrea G. Blum
Often found hanging out with flowers & bees.

#3 Andy Perrin

    Member

  • Members(+)
  • 907 posts
  • Location: United States

Posted 24 November 2017 - 06:40

Is there really any need for such a pricy material in the first place? If it’s going to get all dinged up anyhow, I mean? What’s the advantage of Spectralon?

#4 JMC

    Member

  • Members
  • 148 posts
  • Location: UK

Posted 24 November 2017 - 07:12

Andrea, yes, amazingly useful thanks. Hopefully they are cleanable.

Andy, unfortunately, for some things there is a need. I'm currently writing a paper on some of my UV work and it would have been great to have a range of UV suitable grey tiles for one part of it. Spectralon is optically neutral, so reflects the same in UV and visible (and IR if that's needed) so is a great calibration material. Cost is a problem, but then it often is for calibration materials. They are eye wateringly expensive to buy new, but I try and keep an eye out for second hand equipment from lab clearances. If the sale goes through ok, fingers crossed, I should be getting them for about 15% of the new price.

#5 Cadmium

    Member

  • Members(+)
  • 1,002 posts

Posted 24 November 2017 - 09:07

I wonder how a small ultrasonic cleaner would work on the Spectralon?
Something like one of these, eBay item : 380131255818

#6 JMC

    Member

  • Members
  • 148 posts
  • Location: UK

Posted 24 November 2017 - 11:52

In theory, yes it would be fine (apparently ultrasonic cleaning has been done for PTFE membranes which are very delicate). However I'm not sure I'd like to be the first to try it, unless the other methods of cleaning don't work.

#7 Andy Perrin

    Member

  • Members(+)
  • 907 posts
  • Location: United States

Posted 24 November 2017 - 14:06

Isn’t Spectralon just PTFE, same as what we get elsewhere, just made in a more controlled environment, though? I’m not questioning the need for standards in scientific work, only in general photography. And if you want standards that will hold up scientifically, you will have to validate them via spectroscopy or something after you clean it.

Edited by Andy Perrin, 24 November 2017 - 14:09.


#8 JMC

    Member

  • Members
  • 148 posts
  • Location: UK

Posted 24 November 2017 - 15:44

To be honest I have no idea whether Spectralon is PTFE. I've seen it described as a fluoropolymer, but whether that means it's chemically just PTFE I don't know. Presumably the one with 99% reflectance is pure fluoropolymer, but again having not chemically analysed it myself, that's speculation on my behalf. As for the ones with different reflectances, I'm guessing they add in different amounts of carbon black to the mix before making it - more carbon black, the blacker it is. I asked Labsphere once about making me a custom set with reflectances between 1 and 20%. The cost would have been enormous for anything which wasn't standard in their range, as they'd have to make a large batch even if I wanted a single disk.

I've looked a PTFE alone for reflectance, between UV and IR. It's certainly good enough for most work, but the one I had wasn't as optically neutral as Spectralon across the range of wavelengths. Would it work as a white tile for UV work, yes absolutely. However the complexity comes when trying to get sample which have controlled reflectances which aren't 99%. For my work I needed ones between 0 and 20%. I needed as many as possible in that range to try and develop a calibration curve. In the end I made them from carbon black, magnesium oxide and plaster of paris. It cost me £10 to by the raw materials and took a couple of months to make them once I had settled on a consistent method, and I made 6 targets in that range, enabling me to test my theory. They weren't as optically neutral as I would have liked as reflectance changed a bit with wavelength, but they did the job I needed of them. At the end of the day, if I need to validate what I make against something standard, I need to get my own standards. Even just having a device to measure reflectance, I still need standards to verify what it is telling me. In theory I'd need to get my standards re-verified every year (or however long is recommended) if I'm using them to support other peoples research.

Are these needed for everyday UV photography - in my opinion, not really. A generic PTFE tile would be good enough as a white tile, an Xrite black tile would do the job of a black tile in UV. Getting 'in between' grey tiles would be more difficult, but making your own could be done for minimal outlay, and they would be good enough for most photography. I suppose it depends on how accurate you need it and what you want to do with the data. Most of what I'm doing at the moment is for publication, so for me, these are necessary. Would I have been able to buy them new? No, far to expensive. Would I buy them if I get the chance for a good deal? Absolutely.

Edited by JMC, 24 November 2017 - 15:44.


#9 Andy Perrin

    Member

  • Members(+)
  • 907 posts
  • Location: United States

Posted 24 November 2017 - 16:22

Yeah, then I guess you should probably take a spectrum after cleaning, so you can see how close it is to the manufacturer spectrum?

Regarding the material, I heard sintered PTFE on here I believe.

Edited by Andy Perrin, 24 November 2017 - 16:23.


#10 Cadmium

    Member

  • Members(+)
  • 1,002 posts

Posted 24 November 2017 - 18:53

It is sintered PTFE. Starting with fine virgin PTFE powder, it is put under a specific compression, in a heated oven with a specific temperature.
The powder is compressed at at the same temperature for a given time, which adheres the particles together, but doesn't completely fuse them,
leaving the overall material porous.
The particle size, weight of compression, temperature, and length of time are regulated to maintain the same finished product result from batch to batch.

You can also get powdered PTFE, they offer it many places, but often seen on eBay for pianos.
Powdered PTFE works great for white UV white balance, except that it is not too convenient, because you have to be careful not to spill it, and it can blow away also,
but it can be deep and thick, which is one of the aspects of Spectralon, it is thick and sintered.
Powdered PTFE is basically the same, given thickness.

In my opinion, the main functional difference between sheet PTFE and sintered PTFE is the lack of reflection. It is essentially the difference between shiny paint and flat paint.
Other than that, the material ingredients and process is more closely controlled to assure consistency.

Edited by Cadmium, 24 November 2017 - 19:03.


#11 Andrea B.

    Desert Dancer

  • Owner-Administrator
  • 5,266 posts
  • Location: USA

Posted 24 November 2017 - 19:33

I also have Spectralon standards for investigations in documentary botanical photography. Bjørn and I needed something to use to determine whether we could obtain similar standardized results across different UV platforms (camera + lens + filter + illumination + converter). Yes, we can obtain very similar results across different UV platforms but certainly not identical results. But close enough for all practical purposes of displaying an sRGB JPG online. :D

The Spectralon standards are also useful for determining exposure range of various platforms. Sometimes it is impossible to get the 2% black and the 99% white reflective Spectralon standards equally well exposed in one shot. (I hope that is no surprise to anyone.) Because of the "gamma" curve applied to raw file data, it is also equally sometimes impossible to reproduce in a photograph an "equally spaced" range of tones corresponding to the reflectivity of the 2/25/50/75/99 standards. So you need to decide when using Spectralon standards how you want use them and how you are going to interpret the results. [EDIT: Please see clarification of this rambling of mine in Post #13 below.]

Spectralon is extremely diffuse. That is important for some uses.

I would not use Spectralon powder because of the possibility of accidentally inhaling the stuff.
Andrea G. Blum
Often found hanging out with flowers & bees.

#12 Andrea B.

    Desert Dancer

  • Owner-Administrator
  • 5,266 posts
  • Location: USA

Posted 24 November 2017 - 19:38

Yeah, then I guess you should probably take a spectrum after cleaning, so you can see how close it is to the manufacturer spectrum?

Labsphere has put them thru some pretty rugged tests. Example: left some outdoors for a year or so. After a clean-up, the Spectralon reflectivity was the same. (This does assume no contaminants like dye, oil, etc.)

I should mention that the actual reflectivity does vary by some small amount for Spectralon standards. Mine were calibrated, so I know what that variation is. Variation has to be within a narrow range for a standard to be considered a standard. (we all know this....)
Andrea G. Blum
Often found hanging out with flowers & bees.

#13 Andrea B.

    Desert Dancer

  • Owner-Administrator
  • 5,266 posts
  • Location: USA

Posted 24 November 2017 - 21:03

I think I might need to clarify something that I wrote.

Because of the "gamma" curve applied to raw file data, it is also equally sometimes impossible to reproduce in a photograph an "equally spaced" range of tones corresponding to the reflectivity of the 2/25/50/75/99 standard.

I mentioned this only as a curiosity. When using a reflective standard to judge reflectivity of a photographic subject under a given illumination, it is NOT necessary to physically adjust your photo brightness (HSB model) to "match" the reflectivity of the standard in use. I assumed everyone would understand this, but it is important to clarify this for readers who are not familiar with reflectivity standards.

Here's an example: I photograph my 50% reflectivity standard in a scene. I measure the brightness (HSB) of the 50% reflective standard in the photograph and find it to be, say, 65%. I then look for some subject with 65% brightness in the scene and observe that that subject also has 50% reflectivity under the conditions of which I made the photo.

I enjoy attempting to match brightness to reflectivity in some of my photos because I'm curious just how light & dark the tones "really are" in a UV photo.

If that was clear as mud, kindly advise and I will try again. :D If it is irrelevant or you already know it, kindly ignore. :lol:

I talk too much! It's your turn now. "-)
Andrea G. Blum
Often found hanging out with flowers & bees.

#14 Cadmium

    Member

  • Members(+)
  • 1,002 posts

Posted 25 November 2017 - 12:21

"I would not use Spectralon powder because of the possibility of accidentally inhaling the stuff."

It is not Spectralon powder, it is PTFE powder.
Spectralon is made from PTFE powder that is sintered into a solid block.

It isn't toxic, they use PTFE powder for lubricating all sorts of things, including pianos and other musical instruments.
http://www.howardpia...ne-ptfe-powder/

#15 Andrea B.

    Desert Dancer

  • Owner-Administrator
  • 5,266 posts
  • Location: USA

Posted 25 November 2017 - 16:09

While not toxic, there is always the possibility that inhaled particulates can be damaging to the lungs. (Ever heard of "dust pneumonia"?)
Andrea G. Blum
Often found hanging out with flowers & bees.

#16 Cadmium

    Member

  • Members(+)
  • 1,002 posts

Posted 25 November 2017 - 23:33

You don't need to be worried about PTFE powder. There are way worse things in your house that you use all the time.
The powder is not going to jump out of the container, it will sit there in the container unless you scatter it all over. A lid keeps it sealed up.
I actually have not tried it outside in the wind, so I was over thinking how it does in the wind, just a guess, and it is not toxic.
You are over thinking it, because there is way worse dust that is actually bad for you, and we would not be using this in any way that would scatter it around and get it into our environment at all.
The main concern, like any white balance product, is to keep the material clean and free of other materials that would change the purity and cause an alteration to the original pure white balance.

Edited by Cadmium, 25 November 2017 - 23:37.


#17 Cadmium

    Member

  • Members(+)
  • 1,002 posts

Posted 26 November 2017 - 02:12

Here is more info about PTFE and PTFE power (by DuPont):

https://en.wikipedia...ethylene#Safety

http://www1.mscdirec...19-20110702.PDF

#18 JCDowdy

    JCDowdy

  • Members
  • 1,019 posts
  • Location: Arlington, TN

Posted 26 November 2017 - 05:08

View PostJMC, on 23 November 2017 - 20:48, said:

So, for those that have these things, how easy are they to clean, and what should I not do - scrub too hard, leave to soak, etc, etc?

The only time I did this I followed this procedure except I used RO water (not tap) washed the abrasive paper a bit more thoroughly and wore nitrile gloves.

#19 Cadmium

    Member

  • Members(+)
  • 1,002 posts

Posted 26 November 2017 - 05:38

That is what I would use, RO water, It has a tendency to be 'hungry water', because it is so clean it attracts things to it. Unless they advise against using that.
I know a house window washer, he has a huge RO unit on his truck, uses nothing other than pure OR water. He told me that it is the best thing to clean windows with because the RO water alone removes dirt better.

#20 Cadmium

    Member

  • Members(+)
  • 1,002 posts

Posted 26 November 2017 - 09:21

Because Spectralon is a thick porous mass, it seems to me that it may be possible that dirt in the air, smoke, whatever, might infiltrate the porosity of the substrate, and populate the matrix.
The stuff may get dirty on the inside, below the surface, and the whole point of the structure is to give depth to the whiteness.
Spectralon is PTFE, but powder and other forms of PTFE might actually be a better material, only in the sense that they are more easily and inexpensively replaced with new fresh clean structural depth.
Can you actually clean the Spectralon from the inside out, from under the surface?
Of course PTFE (Teflon) is notorious for being a "non stick surface" (I never cook on it myself, I don't have any cooking equipment using it), but it is supposedly food doesn't get stuck to it, and it is easy to clean.
My experience with handling it and fabricating it, is that it is very slippery in sheet form, and sintered felt has a rubbery feel to it.
However I have pure virgin sheets of it, and they do get dirty to some extent, and things in the air can attach them selves to all sorts of things.

Does anyone have a link to the Labsphere instructions for cleaning the Spectralon? Maybe someone already posted that? I didn't find it.
I have a 4 set, but I have not used it because I don't want to get it dirty until I know how to clean it from the inside out.
It is like $400 for one circle new...

Added: Oh, I found it, thanks John :-)
https://www.youtube....eature=youtu.be

Edited by Cadmium, 04 December 2017 - 02:17.