Conservation and restoration of glass objects is one aspect of conservation and restoration of cultural heritage. The nature and varying composition of the material, and the variety of types of object made from it, demand certain specialized techniques. The conservator needs to be aware of "agents of deterioration" presenting particular risk to glass objects, and how to prevent or counteract their effects. Relevant education and training is available in certain countries through museums, conservation institutes and universities.
The practice of conservation-restoration
Conservation-restoration is the practice of cleaning and discovering the original state of an object, investigating the proper treatments and applying those treatments to restore the object to its original state without permanently altering the object, and then preserving the object to prevent further deterioration for generations to come (Caple, p. 5-6). It can involve many different people from various backgrounds to properly assess and treat an object, such as museum curators, conservators, scientists, and historians. The Metropolitan Museum of Art concludes that "conservators and scientists examine objects in the Museum's collections and those being considered for acquisition to determine their methods of manufacture and chemical compositions, as well as any damage or deterioration they may have undergone... conservators may then perform treatments, such as cleaning, repair, and restoration. They also recommend appropriate conditions for the storage, exhibition, and transportation of objects" (Pilosi and Wypyski, p. 66). Conservator-restorers can be found in museums, private for hire institutions, conservation associations, and government or state organizations. They not only treat glass objects, but also art, metal, ceramics, wood, and various other materials that are in need of preservation.
Historic methods of glass cleaning
Glass has been around since the Egyptian XVIII Dynasty, as the very earliest specimen is a glass bead that has been dated to that time during the reign of Queen Hatshepsut. Glass is very versatile, and there many different types of glass that serve various purposes, such as stained-glass windows, table glassware, and even glass photographic plates. This means that the treatment of these objects depends upon their uses and original purposes. Glass throughout the ages mostly consisted of glass drinking or eating vessels, and then evolved to be part of churches and housing in the form of window glass. According to the Victoria and Albert Museum, most glass is composed of silica (sand), alkali (usually soda or potash), an alkaline earth (lime) and a little waste glass. Other materials, such as lead and barium, could also be added to create a specialized effect in the finished product. Methods of cleaning have evolved from washing with water, to using special chemical cleansers especially made for glass, to even dismantling a large glass object, like a window, to be assessed and cleaned under a microscope in a lab. There was not a need to clean glass thoroughly until glass evolved as part of the 20th-century home, and it suddenly became important to keep glass windows clean and the common cleanser Windex came into the picture in the 1930s. For glass objects that are not window glass, the most common way of cleaning is by water if the glass object is intact and not super fragile. The Victoria and Albert Museum provides guidance about how to go about this way of cleaning. The methods of cleaning may differ if the glass is already damaged, extremely thin or fragile, or very old.
Agents of deterioration
One of the ways in which preventive-conservators address the care of material collections is through assessing risk and needs based on the chief agents of deterioration. Best practices employ the system of "avoiding, blocking, detecting, and responding" to any address threats. By considering these key factors as potential problems with their own needs, stakeholders can make strides in safeguarding assets such as glass objects.
Physical forces to be considered in the preventive-conservation of glass objects can include: "impact, shock, vibration, pressure, abrasion", and may relate to the need to secure both the objects themselves as well as the environment in which they reside.