Paint is used to protect surfaces and it is aesthetically pleasing to the eye. The history of paint begins with cave painters. Natural earth iron oxides and manganese form a mixture called ocher, and provided colors from a light yellow to a deep orange. Animal grease was the binding agent used to provide for a liquid or semi-liquid paint. Some were dense enough to form a primitive crayon. The Egyptians created designs using water colors in a soluble mixture of powdered pigment and gum Arabic and water mixture. Gum Arabic is made from the hardened sap of the acacia trees.
Why Was Lead Used in Paint?
Some watercolors where incorporated into plaster producing various colors that were surprisingly permanent. Paint contains various pigment suspended in a medium. The pigments are minerals or other colorants finely ground and added to a liquid medium or binder. Lead was added to the paint to speed up drying, resists moisture extending the life of the paint and contributes to durability and maintenance of the appearance. However, lead is highly toxic, a fact recognized prior to the Second World War. Lead was banned from paints since 1978.
Latex Paint Definition
Latex is a misnomer because latex paints actually contain no latex, as this is a rubber product. Latex paint is however packed with synthetic polymers. What is a polymer? A polymer is formed by a chemical reaction that creates large molecules containing repeated structural units. Made up of hydrocarbons, polymers occur naturally or are manmade synthetics. Natural polymers include rubber, cellulose and shellac. Celluloid, a synthetic polymer was used as a base for film, but is highly flammable.
Acrylic & Vinyl House Paint
Most house paints are water based labeled as latex or acrylic. Latex is a generic term for acrylic, PVA or vinyl acrylic, styrene and other binders. Binders are the dried paint left behind when dry and hold the pigments that are the color. As does natural latex these synthetic polymers look milky when wet and are clear and flexible when dry, thus these paints are all referred to as “latex” in the US market, and are an “emulsion” in the UK. Vinyl forms the primary ingredient with about 20% acrylics added. The higher the acrylic percentage the better and more expensive the product, so paint makers try to achieve a workable compromise. Acrylics offer superior resistance to water and stains, better adhesion, resist blistering and cracking, are better blockers and resist alkali cleaner prevalent in household cleaning products.
Synthetic Polymer Paint
Synthetic polymers include polypropylene used in milk crates, luggage, and are used to create fabrics (carpets principally contain polypropylene). They also find their way into adhesives, paints, molded items and synthetic rubber and foam. PVC or polyvinyl chloride is used for piping, and of course the modern fabric base, polyester.
Oil & Alkyd Based Paints
Oil based paints contain a high level of organic solvents when compared to latex or water based paints. And like their cousins in the latex-acrylic group, oil is a misnomer. Oil or alkyd paints use synthetic resin as binders. Alkyds are formed using alcohol and organic acids, but may contain triglycerides obtained from usually linseed oil. These alkyd paints are weather resistant and offer high gloss for furniture and household trims. Alkyds offer superior adhesion to the coated surface. These alkyd paints can be applied over nearly any surface even covering latex based paint. Latex paints cannot be painted over alkyd paints as the gloss surface does not promote adhesion for water-based paints. Alkyd paints utilize a solvent, that emit VOC’s or Volatile Organic Compounds that are toxic. Taking longer to dry, needing a well ventilated area for application and depending on solvents and thinners for use and cleanup, these more expensive alternatives to acrylics are even banned in some areas.