How much information appears on the label of a paint tube (or jar) and where it is on a label varies from manufacturer to manufacturer, but good artist's quality paints will typically list the following:
Paints made in the USA have information regarding conformance to various ASTM standards e.g. ASTM D4236 (Standard Practice for labeling Art Materials for Chronic Health Hazards), D4302 (Standard Specification for Artist's Oil, Resin-Oil, and Alykd Paints), D5098 (Standard Specification for Artist's Acrylic Dispersion paints), as well as the required health warnings.
Another common piece of information on a paint tube label is an indication of the series it belongs to. This is the manufacturer's grouping of colors into various price bands. Some manufacturers use letters (e.g. Series A, Series B) and others numbers (e.g. Series 1, Series 2). The higher the letter or number, the more expensive the paint.
Whether a color is opaque (covers up what's beneath it) or transparent is of greatest importance to painters who work with glazes to build up color, rather than mixing on a palette. Not very many manufacturers provide this information on the paint tube label, so it's something you have to learn and remember (see: Testing Opacity/Transparency).
Not all paint manufacturers indicate whether a color is opaque, transparent, or semi-transparent on the tube. Some, like the acrylic paint manufacturer Golden, make it easy to judge how opaque or transparent a color is by having a swatch of the color painted on the label over a series of printed black bars. The swatch also enables you to judge the final dried color, rather than having to rely on a printed version of the color. If you notice some variation in the swatches between tubes, this is because they're painted by hand, not by machine.
Every pigment has a unique Color Index Name, consisting of two letters and some numbers. It's not a complex code, the two letters stand for the color family e.g. PR = red, PY = yellow, PB = blue, PG = green. This, plus the number, identifies a specific pigment. For example, PR108 is Cadmium Seleno-Sulfide (common name cadmium red), PY3 is Arylide Yellow (common name hansa yellow).
When you're faced with two colors from different manufacturers that look the similar but have different common names, check the pigment's color index number and you'll see whether they are made from the same pigment (or mixture of pigments), or not.
Sometimes the paint tube label will also have a number after the color index name, e.g. PY3 (11770). This is simply another way of identifying the pigment, its Color Index Number.
Different countries have different requirements for the health warnings printed on paint tube labels. (Within the USA different states have their own requirements too.) Typically you'll see the word "warning" or "caution" and then more specific information.
An ACMI Approved Product Seal on a paint label certifies that the paint is non-toxic both children and adults, that it "contain no materials in sufficient quantities to be toxic or injurious to humans, including children, or to cause acute or chronic health problems". ACMI, or The Art & Creative Materials Institute, Inc., is an American non-profit association of art and craft supplies. (For more on safety with art materials, see Safety Tips for Using Art Materials.)
The lightfastness rating printed on a paint tube label is an indication of the resistance a hue has to changing when exposed to light. Colors can lighten and fade, darken or turn grayer. The result: a painting that looks dramatically different to when it was created.
The system or scale used for rating the lightfastness of a paint and printed on the label depends on where it was manufactured. Two widely used systems are the ASTM and Blue Wool systems.
The American Standard Test Measure (ASTM) gives ratings from I to V. I is excellent, II very good, III fair or non-permanent in artist's paints, IV and V pigments are rated poor and very poor, and not used in artist's quality paints. (For details, read ASTM D4303-03.)
The British system (Blue Wool Standard) gives a rating from one to eight. Ratings of one to three mean a color is fugitive and you can expect it to change within 20 years. Ratings of four or five means a color's lightfastness is fair, and shouldn't change for between 20 and 100 years. A rating of six is very good and a rating of seven or eight is excellent; you'll be unlikely to live long enough to see any change.
Equivalents on the two scales:
ASTM I = Blue Woolscale 7 and 8.
ASTM II = Blue Woolscale 6.
ASTM III = Blue Woolscale 4 and 5.
ASTM IV = Blue Woolscale 2 and 3.
ASTM V = Blue Woolscale 1.
Lightfastness is something every serious artist should be aware of and decide for themselves how they want to deal with it. Know your paint manufacturer and whether their lightfastness information is to be trusted. It doesn't take much to conduct a simple lightfastness test, other than time. Decide what colors you're going to use from a position of knowledge, not ignorance, about lightfastness. While you may aspire to be listed alongside the likes of Turner, Van Gogh, and Whistler, it's surely not as an artist who used fugitive paints.