Acrylic paint is now one of the most popular painting materials in the art, construction and hobby sectors - many restorers are somewhat more reserved.
History
The first acrylic binder was patented in 1930 as "Plextol"; BASF began industrial production in 1934. From 1946, acrylic paint was also marketed in the USA. At that time, compounds such as xylene or white spirit were used as solvents rather than water; in its present form, the paint has existed in the USA since the end of the 1940s and in Europe since the 1960s. Due to its many positive properties, it quickly became very popular among artists and hobby painters, but also quickly advanced to become the most frequently used paint for both interior and exterior use in the construction industry.
Properties, components and production
The paint is water-soluble when open and can be applied "pasty" or thinned to watercolor consistency with water; after the water escapes during drying (or freezing), the polymers of the binder combine to form a water-insoluble, very resistant layer of rubber-like consistency. Drying time is 20 minutes to 24 hours, depending on the amount of water, humidity and ambient temperature, and the paint is often surface-dry after a short time.
Depending on the pigment contained, the opacity of pasty acrylic paint can vary; the addition of glue or additional acrylic binder can also make the paint more transparent, while the addition of some titanium dioxide can make it more opaque. Reputable suppliers will also always specify the degree of opacity and the pigments used when offering ready-to-use paint. The binder itself is milky when wet, but transparent when dry, which can cause the paint to darken in the drying process.
Pigments, binders, solvents
The two main components of acrylic paint are pigment (which imparts the particular hue) and acrylic binder. Water and sometimes other compounds serve as solvents, which provide a characteristic odor of the open paint - this disappears after drying.
In addition, fillers are often added that can increase the volume or influence the properties of the paint: for example, glue, marble powder or chalk, thickeners, drying accelerators, sand or structural paste. Since the proportion of acrylic binder in commercial paint is quite high, it usually tolerates the addition of up to 50% of its volume of additional substances without any problems. Acrylic paint cannot be mixed with fatty substances, such as oil paint, egg or similar.
Application
The paint adheres to many substrates - metal, wood, plastic, glass and many others - but in the field of fine arts it is probably most often used on canvas. In advance, the pores of the canvas must be sealed before priming, for example with bone or cellulose glue; then one or more layers of primer are applied, often glue-chalk mixtures with increasing amounts of acrylic binder. Ready white primed canvas is also commercially available. The paint can then be applied as desired - thinned or impasto, opaque or glazed. It is possible to apply oil paint to a (completely dry) base of acrylic, but not vice versa!
Acrylic paint in the field of restoration
Since acrylic paint has only been around for a relatively short time, unlike oil paint, egg tempera, or other older techniques, there is no information about long-term changes in the paint's properties, decay processes, and restoration needs. Cracking and yellowing have been recorded in some older works, and it is unclear how they can be addressed.
Therefore, care should also be taken when handling acrylic paint for restoration purposes. Since it is also used as a paint in the building sector, it is sometimes used in the conservation of monuments - but damage can occur here on brittle, porous substrates and especially on wood, which can form mold due to the lack of water exchange. Ideally, the appropriate historic paint should always be used instead of acrylic.
Sealing
Sealing is not actually necessary due to the great durability of the paint, but can be carried out, for example, if the painted surface is to be protected from bumps and scratches. In this case, dispersion varnish is usually used, which is applied with a brush or sprayed.
Advantages and disadvantages
A major advantage of acrylic paint is its easy and extremely versatile processing and long shelf life - it is largely odorless, non-toxic, does not spoil and can be stored at temperatures from 8°C to 35°C and above. Perhaps the biggest drawback is the environmental aspect - like other petroleum-based polymeric substances, the paint is not readily biodegradable and can enter the sea and soil as microplastics. In addition, as mentioned, the long-term properties of the paint are still unknown. In individual cases, the odor of the paint in the open state can be perceived as annoying. In processing, the fast drying time can be a disadvantage, especially when designing large smooth surfaces and color gradients, but this can be countered quite well by thinning with water and / or glue.
