Lead paint

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Lead paint is paint containing lead, a heavy metal, that is used as pigment, with lead(II) chromate (Pb Cr O₄, "chrome yellow") and lead(II) carbonate(Pb C O₃, "white lead") being the most common. Lead is also added to paint to speed drying, increase durability, retain a fresh appearance, and resist moisture that causes corrosion. In some countries lead continues to be added to paint intended for domestic use whereas in others regulation exists that prohibits this, though lead paint may still be found in older properties painted prior to the introduction of such regulation e.g. in the U.S. and the U.K. and Australia. Paint with significant lead content is still used in industry and by the military. For example, leaded paint is sometimes used to paint roadways and parking lot lines.

Toxicity

Main article: Lead poisoning

Although lead improves paint performance, it is a dangerous substance. It is especially damaging to children under age six whose bodies are still developing. Lead causes nervous system damage, stunted growth, and delayed development. It can cause kidney damage and affects every organ system of the body. It also is dangerous to adults, and can cause reproductive problems for both men and women.

One myth related to lead-based paint is that the most common cause of poisoning was eating leaded paint chips. In fact, the most common pathway of childhood lead exposure is through ingestion of lead dust through normal hand-to-mouth contact during which children swallow lead dust dislodged from deteriorated paint or leaded dust generated during remodeling or painting. Lead dust from remodeling or deteriorated paint lands on the floor near where children play and can ingest it.

Regulation

The European Union has passed a directive controlling lead paint use. The United States government banned lead paint by the Consumer Product Safety Commission (16 Code of Federal Regulations CFR 1303).

Lead paint in art

In art, lead white is known as flake white, also sometimes known as Cremnitz white. Flake white is traditionally considered to be the most structurally sound underpainting layer for oil painting, possessing a combination of flexibility, toughness, and permanence not found in other paints, and certainly not in the other white pigments. Genuine flake white is difficult for artists to obtain in many countries, even though other toxic paints (such as the cadmium-based colors) may be readily available. Where flake white is currently available to artists, it is usually only in small tubes designed for painting, not in the larger cans traditionally used for underpainting (coating the canvas prior to the actual painting) which for centuries was flake white's most important purpose.

Artists' use of lead paint is mostly associated with oil painting on linen or cotton canvas. In the relatively rare cases where it has been used in works on paper, it will often become discolored over long periods of time. This is due to the reaction of the lead carbonate in the paint with traces of hydrogen sulfide in the air and with acids, often from fingerprints. As a result, many older works on paper that used lead paint now show some discoloration.

Substitutes

Paint manufacturers replaced white lead with a less toxic substitute, titanium white (based on the pigment titanium dioxide) which was first used in paints in the 19th century. (In fact, titanium dioxide is considered safe enough to use as a food coloring and in toothpaste, and is a common ingredient in sunscreen.) The titanium white used in most paints today is often coated with silicon or aluminum oxides for better durability. Titanium white has been criticized for leading to "chalkiness" when mixed with colors, and the possibility of decreased permanence of organic pigments mixed with it due to its high refractive index.

Zinc white is less opaque than titanium white, and is often seen as a superior white for lightening other pigments in mixtures. Although zinc white is the standard white for the watercolor medium it has long been of debatable permanence in oils. Critics of the pigment argue that its use leads to excessive cracking and delamination, even when very sparingly mixed with other pigments such as lead white.

Some art-supply manufacturers supply a "lead white hue," a mixture, usually of titanium and zinc white, which attempts to imitate the hue of genuine lead paint without the toxicity. It does not, however, have the desirable structural (physical) properties of lead white.

Real estate maintenance and renovation

Humans can be poisoned during unsafe renovations or repainting jobs on housing that has lead paint. Therefore, it is encouraged to carefully stabilize any deteriorated (peeling, chipping, cracking, etc.) paint in a lead-safe manner and take precautions during preparation for repainting.

References

http://www.reuters.com/article/healthNews/idUSTRE57O64G20090825
For further discussion of this issue, see Ralph Mayer's classic work, The Artist's Handbook of Materials and Methods.
Claire L. Hoevel (1985). "A Study of the Discoloration Products Found in White Lead Paint". The American Institute for Conservation: Book and Paper Group Annual. 4.
"Zinc White Problems in Oil Paint". The Smithsonian's Museum Conservation Institute exposes long-term problems with zinc white

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