Copal other copals

As previously stated, there are many other copals found today, and it is hard to distinguish one from another without specialised testing such as infrared spectroscopy. The copals typically have the same pale yellow colour and rough, crazed surface. Although this surface is often removed before the material is polished and sold these copals are seldom worked to any great extent and is sold more as a curiosity. 

Copal esters n. These are normally regarded as the glyceride esters of run Congo copal, although the term can also be applied to esters of other copals. 

In addition to shellac a number of other natural resins find use in modem industry. They include rosins, copals, kauri gum and pontianak. Such materials are either gums or very brittle solids and, although suitable as ingredients in surface coating formulations and a miscellany of other uses, are of no value in the massive form, i.e. as plastics in the most common sense of the word. 

In addition to the minerals, there are also some rock-forming homogeneous materials that have neither the definite chemical composition nor the distinctive crystal structure characteristic of minerals. Such materials cannot, therefore, be considered as minerals and are known as mineraloids. Obsidian, for example, a natural material that has been widely used since prehistoric times for making lithic tools and decorative objects, is a mineraloid. Obsidian has neither a definite chemical composition nor a characteristic crystal structure and is not, therefore, a mineral. Copal and amber are other mineraloids that since antiquity have been treasured as semiprecious gemstones. 

Resins older than 40 000 years are considered to be fossil resins. The fossilization of resins begins with polymerisation and forms ambers and copals. Most of the ambers are derived from components of diterpenoid resins with a labdanoid structure other ambers are based on polymers of sesquiterpene hydrocarbons such as cadinene, and may include triterpenoids less common ambers from phenolic resins derive from polymers of styrene. Figure 1.4 shows the skeletal structures of the components which make up the polymers occurring in fossil resins [141]. 

Lae resin is very difficultly soluble in alcohol, though, like copal, it may be completaly teken up by this advent. Like most of the other resins, It has a strong affinity for bases, with which it forms definite compounds. Dilute hydrochloric acid and acetic acid dissolve the rosin freely, but not the strong sulphurto acid. Borax solutions with the aid of heat also take it up. The portion soluble in alcohol has a specific gravity of 1-139, IIhvekdokbeN found it to be a compound of several rosins, namely—... 

French polish is employed upon flat surfaces, and consists simply ofa solution of resin in spirit of wine. The simplest sort of French polish may be made by dissolving one and a half parts of shell-lao in eight ports of spirit of wine. Such a polish is very durable, but many other gum-resins are employed. A good dark-colored polish is prepared from one pound of shell-lac, half a pound pf gnm-benzoin, and one gallon of spirit of wine. Others reaommend twelve, ounces of shell-lac, three ounces of copal, six ounces of gum-arabic, to one gallon of spirit. 

The name coke is also applied to solid residues obtained from various other carbonaceous materials, such as petroleutn, shale oil, copal, tar, etc (Refs 1, 2, 3, 6, 7, 8, 10 11)... 

Fatty Oil, etc.—Mixtures of colophony (or other resin, especially copal) with resinates, oleates and linseed oil are sold for the preparation of varnishes, and mixtures of colophony with mineral oils, resin oils, fatty oils, solid fats, paraffin wax, ceresine or wax for use as brewers pitch. For the recognition of such mixtures, the following tests may be made. 

Put very simply, copal is young version of amber. There is no definite age at which copal turns into amber, as the process is continuous firom the moment the resin appears on the tree and begins to solidify. In physical terms, when the resin is sufficiently cross-linked and polymerised it becomes amber (see Chapter 13, Plastics ). In other words, the resin has dried out and hardened. This process takes thousands if not millions of years, and not all copal becomes amber as much of it disintegrates with time. Furthermore, as the process is such a long one it is not possible for us to follow it or to replicate it in a laboratory, so there is still much that is speculation. We know, however, that there are some instances of copal that have begun to look like, and take on, the properties of amber. 

Copal is sometimes sold as amber and can be difficult to distinguish, especially for people not used to handling the materials. It is also used as filler or glue in the manufacture of faked amber inclusions, as it has the same colour and specific gravity as amber, and is therefore less easily detected than other materials. 

Amber and copal feel light. This is the most usefiil test when beachcombing for amber, which looks dull and pebble-like in its rough state. In other situations it must be remembered that plastic is also li t. 

Unlike other gem materials, it is common to see swirls and bubbles in amber and copal as the material does not form in the same way as mineral crystals. It is occasionally possible, though rare, to see double bubbles of gas and liquid inside these resins. 

Copal, along with several other plant resins, can be powdered and melted for uses such as varnish, adhesive and in the manufiicture of linoleum. Copal is especially good as a varnish for oil paintings or musical string instruments. 

Plastic materials are sometimes termed resins . These can be synthetic or natural. Copals are natural resins, some of which can turn into amber, given enough time. This happens by an evaporation of some of the chemicals, while other chemicals cross-link and polymerise. 

Other special macromolecules are known, and some were analyzed by pyrolytic techniques. Among these are special gums and lacquers such as mastic, gum elemi, copal, kauri, sandarac, shellac, colophony, amber, etc. [4]. These materials have narrow fields of applications and were not included in this book. 

Earlier chapters focused primarily on an analysis of today s dominant plastic materials, which for the most part, date back to the 20 century. Before that era, not only natural resins, such as beeswax, amber, copal resins, gutta-percha, shellac, bitumen, horn, tortoise shell, and materials derived from cellulose derivatives (cellulose nitrate and acetate), from blood protein (mostly as Bois Durci), or from casein are used to find a variety of applications. Our ancestors used these natural materials to produce, among other things, pieces of jewelry, decorative items, or articles of daily use such as tins, picture frames, or desktop utensils where these materials often replaced metals, wood, paper, or ceramics. 

There are two areas of complication related to analytical pyrolysis in the above-mentioned field. One has to do with sampling and the other with instrumentation. The first is very specific for this particular area of research, while the second will affect any application of analytical pyrolysis. From the point of view of sampling, it is quite obvious that, as with every comparative technique, analytical pyrolysis requires an extensive reference library of pyrograms. This condition can be easily met in case of modem materials, but becomes almost insurmountable when someone is looking for samples of material ranging from a few hundred to a few thousand years in age or, in the case of amber and copal, millions of years. 

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