Lightfastness and other pitfalls
Oct. 11th, 2018 06:02 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
ellerThis is also a follow-up to my post about cheap art supplies, only this time it's not about cheap art supplies but about more expensive ones, in response to a question from jainas about how to recognize whether the paint you buy is lightfast or not. So I decided to write something about the criteria I use when choosing which paints I buy.
Hard criteria: (if something's wrong here, it's a quality problem and I will not buy!)
- Lightfastness
- Availability of pigment information
- Chemical stability
Soft criteria: (paint properties that characterize the paint but that don't tell you anything about the paint's objective quality):
- Organic or inorganic
- Transparent or opaque
- Staining or not
- Granulating or not
I'll go through these criteria one by one and discuss how I approach them. I'm mainly talking about watercolors because they're my main medium. The stuff about pigments, of course, also applies to other materials.
Lightfastness
Lightfastness... Yeah, I pay a lot of attention to it. I'm kind of traumatized because when I started painting, the watercolors I started with had one color that faded horribly (and yeah, that was the infamous Alizarin Crimson which really should come with dire warnings!), and when my family put the paintings I gave them on their walls, all the paintings were ruined. Basically my whole work of two years. Not something I want to repeat!
There are several ways you can look for indicators.
In the USA, there's ASTM lightfastness ratings, they're printed on many art materials. Basically, they use a standardized approach for exposure of paint to light and then rate lightfastness according to how much the stuff they were testing faded. Unfortunately, their testing system is rather rough and only differs between I (okay), II (barely okay, but I already avoid most pigments with that rating) and there are III and IV around, but they're generally so horrible that pigments with these ratings are (with the notable exception of Alizarin Crimson, which seems to be too-traditinal-to-finally-fail) normally not used in professional paints at all.
If we're talking about dyes rather than pigments, there's something called the "Blue Wool Scale" which goes vom 0 (avoid like the plague) to 8 (lightfast). In terms of artists material, I consider anything of 7-8 as "okay" and will not use anything below 7 for serious work. (Interestingly, handprint.com uses this kind of scale for pigments, which is not how the method was originally meant to be used. The results are still interesting and useful, of course.)
Some companies have their own (internal) test methods; in those cases they usually have some kind of scale (for example, the watercolor company whose paints I usually buy uses rows of little stars, from one to five, with 4 or 5 stars meaning reliable pigments, and anything below I consider too questionable to use). The trustworthiness of company-wide lightfastness scales unfortunately depends on the company in question. Some manufacturers' internal ratings are perfectly reliable, but I've also seen some that are completely bogus, so if a company doesn't use ASTM info, you have to additionally check for the pigments in question.
One additional peculiarity is zinc white, which has excellent lightfastness (doesn't fade) but actually becomes more opaque with light exposure. That kind of thing is, of course, impossible to rate with the usual scales. You simply have to know. (Zinc white is to the best of my knowledge the only color that does that.)
Availabilty of pigment information
The pigments are described by a combination of letters and numbers, with the letters giving information about the color and the number of the particular pigment. This will either be printed on the paint tube or be available in the manufacturer's color chart. (If not, don't trust the manufacturer - there is no-one serious around who doesn't at least have this info on their website. Let's consider "PG7" as an example. "Pigment Green Seven" already tells you it's some kind of green. The seven is then something you can look up in a pigment database (for example artiscreation.com is a good one) and find out that we're actually talking about Phthalocyanine Green G, the cooler of the two common shades of phthalo green. (Okay, bad example, PG7 is so common that you probably already knew that without looking it up.) If you're lucky, you'll even find out the pigment you were looking up actually has an ASTM rating. (Careful there, though: with some pigments, lightfastness is not constant but varies from manufacturer to manufacturer. PV23 comes to mind... LOL) Additionally, for watercolors in particular, there's a great site called handprint.com which tests the same pigments from different paint manufacturers. You also have to be careful there, of course - it's about ten years outdated and some manufacturers might have changed their pigment suppliers in the meantime. Still, it's useful to check.
If there's no information at all on your paints - neither a lightfastness rating nor a pigment signifier, it's not reliable artists' material unless you do your own lightfastness tests. Actually... I tend to avoid manufacturers altogether if they don't include pigment listings, simply because a) I assume they've something to hide, and b) I don't like supporting that kind of bad practice. (Actually, there are some suppliers who provide "lightfastness stars" without naming the pigments they used. In that case, you can assume the info to be freely invented. There's no law against bogus lightfastness scales...)
Chemical stability
Sometimes, unfortunately, a high lightfastness rating will mislead you into believing a pigment is safe for use when it's actually not. Lightfastness only tells you whether a pigment fades with exposure to light, nothing more and nothing less. But of course there are also other ways your paint can alterate, for example by oxidation, hydration or chemical reaction with other pigments.
This is something that affects inorganic pigments more often than organic (more about that distinction later) and, unfortunately, it's usually not mentioned by manufacturers at all. So, basically, you either have to rely on your chemical knowledge (if you happen to be a scientist) or consult a database like artiscreation.com about any "peculiarities" a pigment you'd like to use might have.
Examples of lightfast but chemically extremely unreliable pigments include azurite, malachite, rhodonite... Actually quite many natural minerals - which are sold and advertised as "highly lightfast" by some manufacturers without pointing out they'll self-destruct anyway, just not in a light-dependent fashion. I'm not going to comment any further on just what exactly I think of that business practice.
Organic or inorganic
Unless the sections above, this is not a quality criterion. It just refers to whether the pigment is chemically organic (that is, involves carbon in some way) or not. For example, the mentioned PG7 is organic because it involves aromatic compounds. The also very common PB29 (Ultramarine Blue) which is basically a zeolite-type mineral, today usually produced synthetically although you can still find some manufacturers who'll sell you ground Lapis Lazuli if you like spending extra money on no discernible advantage. :)
Please note that organic in this case does not refer to eco-friendly. If you're not a chemist, you'll just have to assume that everything you're using is toxic.
This information is something that's usually not written on the paint itself; you'll have to look it up in a pigment database if you're interested.
Transparent or opaque
Some of the more old-fashioned, dogmatic watercolor guides will tell you this were a quality criterion because watercolor is supposed to be transparent. I happen to disagree there: I have a use for both transparent and opaque colors (so I'll happily buy either; I just want to know the behavior before I use a new color on a painting, LOL) and anyway if you use enough water, everything becomes transparent.
Transparence is usually indicated on paints by a small square that's either empty (for transparent colors), half-empty (for semitransparent colors) or filled (for opaque colors). I should note that sometimes the manufacturer's opinion whether a paint behaves transparent or not differs quite a lot from mine - but since it doesn't matter sooo much, I don't care.
Staining or not
That's something important for watercolorists in particular, it describes whether the color, once it's dried on the paper, can be lifted / washed out again. Organic pigments tend to be more staining, but that's not a universal rule. (Still, it's one of the reasons I buy mostly organics.) This is also not a quality criterion but rather depends on which technique you're trying to use.
If you (like me) want to use several layers of color over each other, staining colors are an advantage because you don't want the first layer of color to run all over the place when adding the second one. So, for multi-layered work, staining colors are preferable.
If you however work with only one color layer, and it's important to you to wash out some highlights later, you'll probably be happier with the non-staining colors.
This information, however, is not given by most manufacturers - and in the case of the one professional manufacturer that actually gives a staining scale, I've often found the information to be wrong. Unfortunately, it also doesn't only depend on the pigment alsone but also the manufacturer's pigment processing, so a color might be staining from one manufacturer and non-staining from another. So I'm basically relying on personal experience only.
Granulating or not
Granulation describes the funny thing that some pigments (like Ultramarine Blue or Lunar Black) do when small color particles lump together and create a bit of a grainy texture on the paper. Whether you want this to happen or not is purely a matter of taste.
I've however found that granulating pigments (which are usually non-staining by nature) only really work if you don't overpaint them again. So they're clearly misplaced in an underpainting over which you want to add other layers. If I use them (which I do only rarely) they're usually in the last layer I do (before highlights).
Um, yeah, hope this helps...
jainas about how to recognize whether the paint you buy is lightfast or not. So I decided to write something about the criteria I use when choosing which paints I buy. Hard criteria: (if something's wrong here, it's a quality problem and I will not buy!)
- Lightfastness
- Availability of pigment information
- Chemical stability
Soft criteria: (paint properties that characterize the paint but that don't tell you anything about the paint's objective quality):
- Organic or inorganic
- Transparent or opaque
- Staining or not
- Granulating or not
I'll go through these criteria one by one and discuss how I approach them. I'm mainly talking about watercolors because they're my main medium. The stuff about pigments, of course, also applies to other materials.
Lightfastness
Lightfastness... Yeah, I pay a lot of attention to it. I'm kind of traumatized because when I started painting, the watercolors I started with had one color that faded horribly (and yeah, that was the infamous Alizarin Crimson which really should come with dire warnings!), and when my family put the paintings I gave them on their walls, all the paintings were ruined. Basically my whole work of two years. Not something I want to repeat!
There are several ways you can look for indicators.
In the USA, there's ASTM lightfastness ratings, they're printed on many art materials. Basically, they use a standardized approach for exposure of paint to light and then rate lightfastness according to how much the stuff they were testing faded. Unfortunately, their testing system is rather rough and only differs between I (okay), II (barely okay, but I already avoid most pigments with that rating) and there are III and IV around, but they're generally so horrible that pigments with these ratings are (with the notable exception of Alizarin Crimson, which seems to be too-traditinal-to-finally-fail) normally not used in professional paints at all.
If we're talking about dyes rather than pigments, there's something called the "Blue Wool Scale" which goes vom 0 (avoid like the plague) to 8 (lightfast). In terms of artists material, I consider anything of 7-8 as "okay" and will not use anything below 7 for serious work. (Interestingly, handprint.com uses this kind of scale for pigments, which is not how the method was originally meant to be used. The results are still interesting and useful, of course.)
Some companies have their own (internal) test methods; in those cases they usually have some kind of scale (for example, the watercolor company whose paints I usually buy uses rows of little stars, from one to five, with 4 or 5 stars meaning reliable pigments, and anything below I consider too questionable to use). The trustworthiness of company-wide lightfastness scales unfortunately depends on the company in question. Some manufacturers' internal ratings are perfectly reliable, but I've also seen some that are completely bogus, so if a company doesn't use ASTM info, you have to additionally check for the pigments in question.
One additional peculiarity is zinc white, which has excellent lightfastness (doesn't fade) but actually becomes more opaque with light exposure. That kind of thing is, of course, impossible to rate with the usual scales. You simply have to know. (Zinc white is to the best of my knowledge the only color that does that.)
Availabilty of pigment information
The pigments are described by a combination of letters and numbers, with the letters giving information about the color and the number of the particular pigment. This will either be printed on the paint tube or be available in the manufacturer's color chart. (If not, don't trust the manufacturer - there is no-one serious around who doesn't at least have this info on their website. Let's consider "PG7" as an example. "Pigment Green Seven" already tells you it's some kind of green. The seven is then something you can look up in a pigment database (for example artiscreation.com is a good one) and find out that we're actually talking about Phthalocyanine Green G, the cooler of the two common shades of phthalo green. (Okay, bad example, PG7 is so common that you probably already knew that without looking it up.) If you're lucky, you'll even find out the pigment you were looking up actually has an ASTM rating. (Careful there, though: with some pigments, lightfastness is not constant but varies from manufacturer to manufacturer. PV23 comes to mind... LOL) Additionally, for watercolors in particular, there's a great site called handprint.com which tests the same pigments from different paint manufacturers. You also have to be careful there, of course - it's about ten years outdated and some manufacturers might have changed their pigment suppliers in the meantime. Still, it's useful to check.
If there's no information at all on your paints - neither a lightfastness rating nor a pigment signifier, it's not reliable artists' material unless you do your own lightfastness tests. Actually... I tend to avoid manufacturers altogether if they don't include pigment listings, simply because a) I assume they've something to hide, and b) I don't like supporting that kind of bad practice. (Actually, there are some suppliers who provide "lightfastness stars" without naming the pigments they used. In that case, you can assume the info to be freely invented. There's no law against bogus lightfastness scales...)
Chemical stability
Sometimes, unfortunately, a high lightfastness rating will mislead you into believing a pigment is safe for use when it's actually not. Lightfastness only tells you whether a pigment fades with exposure to light, nothing more and nothing less. But of course there are also other ways your paint can alterate, for example by oxidation, hydration or chemical reaction with other pigments.
This is something that affects inorganic pigments more often than organic (more about that distinction later) and, unfortunately, it's usually not mentioned by manufacturers at all. So, basically, you either have to rely on your chemical knowledge (if you happen to be a scientist) or consult a database like artiscreation.com about any "peculiarities" a pigment you'd like to use might have.
Examples of lightfast but chemically extremely unreliable pigments include azurite, malachite, rhodonite... Actually quite many natural minerals - which are sold and advertised as "highly lightfast" by some manufacturers without pointing out they'll self-destruct anyway, just not in a light-dependent fashion. I'm not going to comment any further on just what exactly I think of that business practice.
Organic or inorganic
Unless the sections above, this is not a quality criterion. It just refers to whether the pigment is chemically organic (that is, involves carbon in some way) or not. For example, the mentioned PG7 is organic because it involves aromatic compounds. The also very common PB29 (Ultramarine Blue) which is basically a zeolite-type mineral, today usually produced synthetically although you can still find some manufacturers who'll sell you ground Lapis Lazuli if you like spending extra money on no discernible advantage. :)
Please note that organic in this case does not refer to eco-friendly. If you're not a chemist, you'll just have to assume that everything you're using is toxic.
This information is something that's usually not written on the paint itself; you'll have to look it up in a pigment database if you're interested.
Transparent or opaque
Some of the more old-fashioned, dogmatic watercolor guides will tell you this were a quality criterion because watercolor is supposed to be transparent. I happen to disagree there: I have a use for both transparent and opaque colors (so I'll happily buy either; I just want to know the behavior before I use a new color on a painting, LOL) and anyway if you use enough water, everything becomes transparent.
Transparence is usually indicated on paints by a small square that's either empty (for transparent colors), half-empty (for semitransparent colors) or filled (for opaque colors). I should note that sometimes the manufacturer's opinion whether a paint behaves transparent or not differs quite a lot from mine - but since it doesn't matter sooo much, I don't care.
Staining or not
That's something important for watercolorists in particular, it describes whether the color, once it's dried on the paper, can be lifted / washed out again. Organic pigments tend to be more staining, but that's not a universal rule. (Still, it's one of the reasons I buy mostly organics.) This is also not a quality criterion but rather depends on which technique you're trying to use.
If you (like me) want to use several layers of color over each other, staining colors are an advantage because you don't want the first layer of color to run all over the place when adding the second one. So, for multi-layered work, staining colors are preferable.
If you however work with only one color layer, and it's important to you to wash out some highlights later, you'll probably be happier with the non-staining colors.
This information, however, is not given by most manufacturers - and in the case of the one professional manufacturer that actually gives a staining scale, I've often found the information to be wrong. Unfortunately, it also doesn't only depend on the pigment alsone but also the manufacturer's pigment processing, so a color might be staining from one manufacturer and non-staining from another. So I'm basically relying on personal experience only.
Granulating or not
Granulation describes the funny thing that some pigments (like Ultramarine Blue or Lunar Black) do when small color particles lump together and create a bit of a grainy texture on the paper. Whether you want this to happen or not is purely a matter of taste.
I've however found that granulating pigments (which are usually non-staining by nature) only really work if you don't overpaint them again. So they're clearly misplaced in an underpainting over which you want to add other layers. If I use them (which I do only rarely) they're usually in the last layer I do (before highlights).
Um, yeah, hope this helps...
no subject
Date: 2018-10-12 05:02 pm (UTC)