Saturday, September 14, 2013

UPDATE! Standard Specification for Artists Pastels

This is my 2,500th blog post on Making A Mark and my instinct was to make it both a serious one and one about 'making a mark'.

How better than an update on progress towards a Standard Specification for Artists Pastels?  This focuses on one of my favourite art media (see my website Pastels and Pencils) and, in particular, on one of my favourite topics - the lightfastness of artist materials.

Pastels in L. Cornellisen & Sons in London

The Standard Specification for Artists Pastels


Here's the current statement of what the Standard Specification for Artists Pastels will cover when published.
1. Scope This specification establishes requirements for composition, performance, and labelling artists pastels. This specification includes requirements for identification and lightfastness. Pastel specimens are exposed to both natural daylight through window glass and simulated daylight window glass-filtered radiation to determine the lightfastness rating for each pastel. No standard currently exists for pigments, chalk and a light binder that keep the sticks together to be used for drawing or painting on a sanded or other gritty substrate.

Keywords Pastel, pastels, chalk, substrate, pigment, shades, tints, sanded paper, colored sticks, soft pastels, hard pastels, conte crayon, color mixing, light fastness

It doesn't exist as yet but there is a working group developing it.  I've been having a very interesting email conversation about it recently part of which is duplicated below.

This is going to be of most interest to pastel artists AND those interested in lightfastness and pigments.  It touches on standards relating a to range of art media and lightfastness testing generally.

It will get technical - but hopefully I'm filtering out most of the too techie aspects and/or including links to more information.

My big interest - for a long time - is in the lightfastness aspects of art materials testing and how art materials can be tested in efficient and cost-effective ways which produce reliable indications of which brands meet the standard as defined.

You'll see as you read on why this is easier said than done!

I'm going to reproduce the question and answer format used in my email correspondence - in part because that's how I found out what I now know.

Do let me know if there is anything you don't understand and I'll either try revising how I'm conveying the information or consult my correspondence to see if it contains a better answer.

I'd add that I found I understood it all much better reading through some of the answers I got for a second time!

Don't hesitate to ask questions or comment.  I'm going to be sending a link to this blog post to the people who look after the Committee which sets the standard. I'm sure they will find your perspective useful.

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Who creates the Standard Specifications for Artists Materials?


The responsible body is ASTM International. This was formerly known as the American Society for Testing and Materials (ASTM). (see also Wikipedia ASTM International).  Essentially it's industry and scientific based with input from expert consumers.

The responsible committee for paint and pigment based media used by fine artists is the Subcommittee D01.57 on Artist Paints and Related Materials.
ASTM D01.57, the Subcommittee on Artists' Materials, helps artists and consumers recognize product quality and safety when manufacturers' products conform to its Standards.

D01.57 has about 60 members representing consumers and manufacturers of artists' materials. Members of the Subcommittee include artists, educators, conservators, medical doctors, chemists and other materials scientists, and representatives from art materials manufacturers, artists' groups, manufacturers of testing equipment, and regulatory agencies. Its meetings, held twice a year, are open to anyone who wishes to attend - but those who wish to vote during the standards-writing process must be members of ASTM.

A Narrative Summary of ASTM International Standards Pertaining to Artists’ Coloring Materials 
This reports to the ASTM Committee D01 on Paint and Related Coatings, Materials and Applications was formed in 1902. (see Info Sheet - pdf file)

To date Subcommittee D01.57 on Artist Paints and Related Materials has produced 16 standards which are active today.   These include standards for almost all the common art media used by fine artists (see below) EXCEPT for pastels:
The standards are a priced publication and are not available free of charge.

Where are we up to with the new Standard Specification for Artists Pastels?


The task group is still working on the draft of this standard. There have been two draft so there is some progress.

The Staff Manager at ASTM is Jeffrey Adkins.  Click the link on the webpage to get his email address.

The Technical Contact is Michael Skalka and he is most informed as to progress to date. I have his email address but he can also be reached via Jeff Adkins. [NOTE: Michael Skalka is the Conservation Administrator, National Gallery of Art, Washington, DC 20565]

What follows is in essence an email conversation between me and Michael Skalka. I have to thank Michael profusely for the time he's taken to answer my very detailed questions.  I now understand the issues which present challenges for the ASTM so much better. I also thank him for allowing me to share them with the many pastel artists who read this blog.

Normal text is me - and this is the response from Michael Skalka indented as a quotation.

How does ASTM test for quality in art media?

The crux of a quality standard rests on several factors. This is a common theme for nearly all our art materials product standards. They are the following: 
  • light fastness of the pigments, 
  • revelation of the pigments used by common name and Color Index number, 
  • stating the identity of the binder used, 
  • providing conformance to hazardous materials warning (that is a mandatory standard for all US imported and domestic art materials - ASTM D4236) and 
  • conformance to uniform labeling of the above mentioned items in a uniform fashion either on the product container or accompanying literature.
In other words, the standard follows a pattern which is repeated for all art media according to a scientific perspective on what manufacturers - and artists - need to know.

How does ASTM test for lightfastness?  Surely all art media use the same pigments at end of the day?

Testing the light fastness of pigment is the key for all our existing art materials standards (oils, alkyds, acrylics, watercolors, colored pencils) They don't all use the same pigments. Some pigments are oil loving. Some pigments are adverse to being mixed in water, etc. Many are the same, but not all. Example: you won't find lead white acrylics.
This was news to me - in the sense that not all media can use the same pigments.

How does the standard impact on how pastels are made?

We don't dictate a specific recipe for making pastels or any other art product. We just create the "measuring device" to determine product quality. Purchasing a standard is not a "how to" guide to making an art materials. It tells them how to test for light fastness via sample preparation. How to measure samples and how to compile the data to create lightfastness ratings. The standard also spells out labeling requirements. Manufacturers take pride in devising there own method of making art materials and that signature look and feel creates the diversity everyone appreciates in brands that are available.

How do you test for how the pigment in a pastel is laid down?


For example, do you have a defined "recipe" for how that pigment is mixed with other materials to produce a pastel stroke on a defined type of support?

Also how do you take account of the different types of sub-strata that pastel artists use (eg art paper and more abrasive surfaces) which affect how they make strokes and hence how the pastel reacts to light?
In a ideal testing world, we would not have the need for a substrate. We would just test the pastel material alone.

It is important not to confuse the artists' use of materials and the technique they may employ with the testing of the quality of the material.

Frankly, we don't care how the artist uses a material even though we would strongly recommend a variety of best practices to achieve long lasting results.

We are experimenting with the use of a small size Petri dish container that we would pack with pastel powder to test the lightfastness of the pigment and its constituent components.

Many of the papers we have tested behave badly when exposed to 1260 megajoules per meter squared of light energy exposure. They turn medium to dark brown and that in turn influences the spectrophometer reading we need to take to determine the amount of change in the pastel after it is exposed to light
The latter response made me smile. I'm forever telling people that the pastels done by some of the past masters have to be kept in low light because of the paper not the pastels!

I can well understand the attractions of a petri dish. Getting away from a substrata altogether eliminates that as an element which might confuse test results. Presumably it's also possible to measure how far any deterioration in colour has penetrated the depth of pigment powder in a petri dish?

How can an artist tell how good the pastel stick is?


Testing a pigment won't tell you "how good" or "how lightfast" an individual pastel is - but this is actually what the artist wants to know! A good standard needs to be useful for the people who are the end users. Pastel artists need to know whether they are using archival quality pastels in artwork sold to art collectors.
One of the tenants of art materials testing is the long term stability of the colors artists' employ to make works of art. All of our consumer and manufacturer partners agree on this point. We have good data from years of testing experience that exposure to light at the levels we determined (1260 megajoules per meter squared) is a robust test of the stability of a pigment in a selected binder. Again, our standards facilitate manufacturers to aid in selecting pigments that have been properly tested to assure they are light fast. It is the manufacturer's responsibility to take that information and turn it into a quality art material with all the components that need to be included that create the best working properties.
I conclude from this that principle beneficiary of the standard is the manufacturer - who gets information in the  (priced) standard which specifies which are the pigments judged to be stable in the long term and therefore suitable for works of art.

The information about lightfastness is limited to the pigment used and does not relate to the quantity used in the pastel. (At this point I began to think about food labelling and how items must contain a certain percentage of a food before being entitled to be labelled as representative of that foodstuff - see my example below.)

Can the standard make a practice oriented statement which connects the medium to the practical experience of the pastel artist?

None of the ASTM art materials standards address how artists use the art media.

We do not have the right to dictate our vision of the proper use of an art material to the artist.

Our standards address artist quality art materials so the implication here is that the manufacturer is employing light fast pigments, has a high pigment load to binder ratio, is not adulterating the pigment with fillers or unreported colorants to enhance the hue.

The standard also included guidelines for proper labeling that allows the artist to understand the pigments used and the binder mixed with them.

ASTM is not an enforcement agency. We do not police the use of standards or quality manufacturing. All the standards with the exception of D4236 which is US Federal law, are voluntary standards. We encourage manufacturers to comply and try to make the standard easy to read and follow.
For me, the fascinating word in the above response is "implication".  I'd be happy with a situation where it's recognised best practice to state precisely what the pigment percentage load is in any pastel.  I wouldn't want to see a manufacturer claiming compliance with a standard i.e. they use an accredited pigment suitable for the media - but the pastel stick does not have a high pigment load and/or is adulterated with fillers or other colorants. It would be nice to assume all manufacturers follow best practice - but not all do.

Does the standard need to make a statement about how much pigment is used?


Any experienced pastel artist will tell you that they always know the difference between a pigment rich dry medium and one which has less pigment.  It's not about how soft a pastel is, it's about the quality of the colour.
This will always be a subjective judgement on the part of the artist. Many organic pigments must be throttled back with some form of inert filler to make the pigment balanced with other weaker or inorganic pigment that do not have the same strength. In oils, every phthalocyanine blue or prussian blue paint must be mixed with a filler or the color would overwhelm the palette. But that is a bit off the topic. Quality of color is more about selecting pigments with the right compatibility for pastel. Pigments are purchased with particle size in mind. They may be coated or uncoated. They have enhancement that manufacturers of pigment put in them to maintain stability or harmony in certain media. The pigment industry is not focused on the needs of art. All pigments are made for industrial purposes and smart art material manufacturers learn to know what pigments to select to get the best results.
I definitely want to know how much "filler" there is as well as how lightfast the pastel is.
That information is not available. It is proprietary information related to the formula that the manufacture worked hard to create. Besides, other than the masstone, all pastels will be mixed with white chalk/clay or pigment to ramp the color up as a tint or down as a tone so pastels are a bad example to cite for the use of what is by nature of the media a method for making tint/tone mixtures.
It's absolutely no use whatsoever to artists if a manufacturer can boast about making use of lightfast pigments if they are also using pigments which may be cheaper and less lightfast as well as other "fillers" to pad out any expensive pigments in an individual pastel stick. (An analogy - Think of it a bit like the labelling of the constituents on packets/tins of foodstuffs etc - where the percentage of each constituent has to be identified. This is when you find out just how much sugar gets added into yoghurt to make people buy more!)
The one nice thing about using poor cheap ingredients is that artist will quickly figure out that this is the case by use of the product. So much of art material are sold by word of mouth recommendations so a manufacturer looking to make a quick profit on cheap products will see sales plummet as artist figure out that the material is poorly made. Cheaper pigments don't equal light fastness. Like any other marketplace, pigments with robust working properties like lightfastness are expensive. Pigments are the most expensive part of manufacturing, followed by labor.
The secrecy between manufacturers of dry media as to the nature of the constituents of their products is quite profound. I already know which pigments are lightfast from other testing processes - the issue is how much lightfast pigment is used. I have tried asking manufacturers to tell me which pigments they use in their pastel sticks - with no success.
This issue will not change with the adoption of a pastel standard. If a pastel manufacturer is not interested in revealing the pigments used, they won't be interested in adopting the pastel standard. The standard requires labeling of the product just like oil paints, with the pigments and binder used.
My feeling is that the manufacturers making the better quality pigments will follow the standard - in part, in order to substantiate claims made as part of the marketing of pastels.

Why should dry media manufacturers be so silent when the paint manufacturers are now much more forthcoming? It just makes me suspicious. One can only surmise that it's the percentage proportion of non-pigment media which makes a difference to their bottom line!
Again, the nice thing about pastels is that use of a product tends to reveal the nature of the pigment load and quality of manufacturing. As stated before, pastels are a bad example to use regarding any adulteration of the media since the formula for pastels is pigment, chalk, clay, pigment to tint or tone a color, a gum to hold it together and water which disappears from the mixture when the pastel dries.

On the economic side of the business, making pastels is a money intensive operation and savvy producers learn to find the best pigments at the best price, keep labor costs low and produce products of quality. If they don't they will need to charge too much for the market to bear the price and the product won't sell. Pastel makers are both large and small so making them and not having to charge a fortune to buy them is paramount. It is hard for small operations to compete with the larger art materials manufacturers in the pastel market because small producers don't have a lot of capital to invest, equipment is minimal so that means a lot is done by hand.
The interesting thing I find repeatedly from my surveys of favourite pastels is that the more expensive pastels tend to do well. That suggests to me that pastel artists can always tell which pastels have a high pigment load and which do not - and they are well informed pastel artists are prepared to buy the best.

Can a standard define the nature of the labelling eg define what percentage of lightfast pigment is used?


In my view this means that if the standard is to comment on the pigment, then the manufacture of any pastel wanting to be defined as using a lightfast pigments MUST declare what percentage is attributable to a defined LIGHTFAST pigment as opposed to other media and/or other non-lightfast pigments (ie it's not enough to declare what percentage is attributable to pigments alone - the defined percentage must relate to the lightfast pigment(s) alone.)
You touch on a basic conundrum in making and testing pastels. First, pastels are going to be tested as finished products, not as individual pigments. Pigment mixtures will be tested as the combination of pigments and testing shows that if one of the pigments fail, the degree of change will render the pastel to be rated as less than outstanding in terms of lightfastness. It would be stupid for a manufacturer to use a light fast pigment and a fugitive pigment in a pastel and subject it to the pastel standard test. The fugitive pigment would fade and the pastel stick would fail to be light fast.

Regardless of the percentages and the amount of other ingredients, the pastel mixture must stand together to be tested to determine its light fastness. Robust ingredient will pass and others will fail. In many several unusual cases, a light fast pigment when mixed with another light fast pigment has failed because of chemical interaction between pigments. So it is really the mixtures that need to be the focus of much of the testing.

OK, the conundrum - Take a very high value pale yellow pastel. It is made of very little yellow pigment and a lot of white pigment, chalk or clay to achieve the light tint. Many of these types of mixtures fail because they have so little pigment load in them. They are hard to measure with a spectrophotometer because they almost appear faded even before exposure and the span of potential change is so narrow. We don't face this issue with any other medium. In oils, acrylics etc, light value colors are derived from full strength pigments mixed by the artist with white. In pastels, the manufacturer does the initial mixing to create a light tint.

Are some voices more vocal that others in the process of determining the standard?


I rather suspect those with an eye on the bottom line protest rather more than most about the cost of testing. That was certainly the impression I had with respect to the testing of coloured pencils.
Ironically, our most vocal pastel manufacturer complaining about the cost of the test is marketing the most lightfast and robust line of pastels in the industry. So it is all about wanting to conform to the standard but not wanting to pay $150,000 or more, to do it.
I don't think it's the cost of testing which matters to a manufacturer so much as the impact on their profit line if their pastels are 'outed' as less good quality when compared to other pastels.
Funny you should mention this. Whenever we adopt a standard we conduct a round robin test to see the current state of the marketplace. We do a light fastness test on existing pastels. We share the results of the testing with the manufacturer. In almost every case, the manufacture is thankful for the free data from the test and immediately adjusts formulas to make the pastel conform and pass the light fastness test. Regarding pastels, a lot of manufacturers don't have the funds to do testing and have gone entirely by the very poor blue wool testing that the pigment manufacturer uses to sell colorants. Again, mixtures are important so a pigment that performs fine with the blue wool test may not do as well when made into a finished pastel stick. Most manufacturers don't test for light fastness of finished products so that is why having a standard that can be used helps the industry. A few conform to the standard. Others feeling that they might miss out on sales, conform as well. Lots of oil paint manufactures do not conform to the letter of the law regarding the oil paint standard, but because others do, they adopt many if not all of the points made in the standard to retain a competitive edge in the marketplace.
This was all really good news. We can all look forward to better standards of pastels across the board!

Has every pastel manufacturer had a voice about the standard-setting process.


For example, there are a lot of small artisan pastel-makers - however most have very little market share. The costs of testing might be expected as having most impact on them.

However if I was an artisan pastel maker with a focus on quality not mass production I'd want to devote resources to having my pastels tested so that I could demonstrate how high quality they are - and why they should earn more market share - with a consequential impact on the artisan company's profit line.
Focus on quality – sounds good until you work out your business plan and if you are not a smart raw materials shopper you find that you only break even by selling your product 40 percent higher than your competitors. Most new manufacturers chew through several hundreds of thousands of dollars before they make a profit. It is a tough business. Only after one becomes established and cultivates brand loyalty that one sees a profit and light at the end of the tunnel. Oh, and just remember, most consumers want art materials at the cheapest possible prices. We found that out in the US by the infiltration of cheap imports. It is driving our canvas manufacturers out of business. Why pay $6.00 for a small canvas when one can pay $3,00 for 2 bundled canvases. So you get two for half the price when buying imports. Discount internet sales are also shaping the US market with deep discounts on everything because they buy in such volume and don't operate a brick and mortar store.
I have long preached the value of supporting your local quality B&M art store - use it or lose it!

It strikes me that one of the very important words in the Statement will be "Artists" - meaning something along the lines of "artist grade pastels as used by an artist selling an artwork of archival standard which will not deteriorate for many decades".  In other words cheaper pastels targeting the hobby market could not claim the description "artists' grade pastels"

How are pastels tested?

The number of tests has a real cost value associated with it.

Specific to pastels, testing of finished color samples can mean that a company might be responsible for running 3 tests on each sample with a typical color line numbering 250 to 300 colors, based on all the tints and shades. The volume of tests could make conformance to the standard such a costly proposition that no manufacturer will be able to afford the test. In response, the subcommittee is considering the creation of a table of individual pigments tested by the subcommittee to be published with the standard that will provide a cost and time savings measure for manufacturers. If this approved set of tested samples is adopted by the group, it will require the subcommittee to commission testing of documented pigments using the pastel test method we devised to determine the light fastness level. Publication of the light fastness levels would include only the pigment name, CI name and CI number and the light fastness rating. No brand specificity would be published.

When do you expect the testing to be completed?

If the statistical number of samples can be agreed upon to provide some confidence in the test for light fastness, that will take little time to accomplish. The time factor that will delay approval of the standard will be deciding on providing a table of tested samples, determining which colors will be tested and how the samples will be prepared needs to be resolved. If this can be done before the January 2014 meeting, we will be able to take advantage of the winter "window" of opportunity for outdoor Arizona testing that will be required. That would allow us to move the standard further to completion by having data interpretation completed by the spring of 2014. If not, it might delay the testing for an additional year.

Overall, the standard might be ready for submission for approval via ASTM voting by late summer 2014 or if problems arise, about a year later.
There are some related issues which are very technical relating to sampling size which I've omitted from the response.

Will you produce a "proxy" test for testing the lightfastness of pastels?


PLEASE devote some resources to determining a standard "proxy" test (e.g. a blue wool test) which any artist or pastel art society can use for testing their own pastels - in their own environment.
Lucky, two test method already exists. They are called D5398, Standard Practice for Visual Evaluation of the Lightfastness of Art Materials by the User. This allows an artist to test any media using blue wool as a guide to determine when the samples have had enough light energy exposure.

The other is a technical test that requires a spectrophotometer to do the measuring. That test is D5383 Standard Practice for Visual Determination of the Lightfastness of Art Materials by Art Technologist.

Again, the test for the pastel standard will be a manufacturers guide to making light fast, properly labeled pastels and would be of little to no interest to the practicing artist. The test focus a lot on the light fastness testing using instrumentation to determine the change in pre-exposed and exposed samples.

Please bear in mind that, other than the one brand of coloured pencils that bears the ASTM number (Caran d'Ache Luminane),  the only practical information that coloured pencil artists have about the lightfastness of coloured pencils is the workbook produced by the CPSA. This is based on testing which is a proxy of the full scale testing defined by the standard. This, in essence, is all artists need. 

PLEASE consider enrolling pastel artists around the world in testing pastels.


This might also help address the issue re costs and sample size if enough artists agree to undertake tests to a defined "recipe". I know the Arizona light gives the fastest / best results - however the vast majority of pastel art will never ever encounter the intensity of light experienced in Arizona!

[Note: We had an extended and technical conversation about sample sizes for testing the "proper" way which I won't reproduce here - but which led to the above comment!]
Official testing requires the tester to have the following: Indoor testing – a bench top or free standing light exposure machine. These units made by Q-Lab and Atlas start at $25,000 USD and up. One also needs a spectrophotometer to test the carefully prepared sample before and after the light exposure. The machines and the time needed are out of the league of a majority of artists. Outdoor testing – this needs to be done in central Arizona where we have documented measurement of the sun intensity. Samples need to be prepared similar to the indoor test, measured with a spectrophotometer before and after exposure and the samples must be exposed outdoors in a ventilated test box built to ASTM specifications. Exposure is done at a 45 degree angle and an instrument needs to be included in the test that measures when the samples reach 1260 megajoules /m2. Cost for this is roughly $8,000 for the spectrophometer, $15,000 for the energy measuring unit, $1,500 for the test box, $1,500 for the rack to hold the test box.

So, as you can see we employ test services to do the precise work of exposing samples and measuring the samples for this work. Manufacturers would do the same.

Arizona: Even our members question this practice. I remind everyone that all we are doing is "borrowing" natural light to expose a sample to the effects of the full spectrum of UV, Visible and Infrared energy. It is not how pastels will be displayed but we don't have 100 years to wait to test samples in normal ambient conditions so we do accelerated testing to shorted the time needed to see results. Light absorption is cumulative so we are speeding up the process. Fundamental testing resolved that if something is going to fade it will do so by the time it is exposed to 1260 megajoules per m2. That is roughly what blue wools are geared to do as well. We use a particular latitude designation in Arizona because in the US it has the most consistent daily light exposure, lowest humidity of anywhere in the US. Florida is another test site but that has high humidity and that influences sensitive media like pastels. We are just borrowing freelight to conduct the test. We did round robin test in northern Virginia and the results take longer to obtain and don't correlate as well with the Arizona or Florida tests. The idea is to control as many variables as possible so that the results don't get skewed.
Well it seemed like a good idea!

Anybody who fancies doing their own tests would be well advised to purchase D5398, Standard Practice for Visual Evaluation of the Lightfastness of Art Materials by the User.

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I hope you've found this to be as fascinating and informative as I did - even if you're not a pastel artist!

If you do have any comments or queries please leave a comment below.


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1 comment:

Meera Rao said...

Congratulations! That's is some achievement ! And best wishes for another 2500 at least ;) you blog posts always interesting and enlightening!



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