“The Age of Wood: Our most useful material and the construction of civilization,” by Roland Enos, Scribner, NY, 2020. This 318-page hardback tells the story of wood. Wherever trees were available wood was the preferred construction material for eons. When not grown locally prosperous communities like Egypt imported it.
After a brief introduction on the properties of wood cells that account for compressive strength and flexibility, Enos reviews archeological finds to show how wood use changed over time. In the early days, woodworking tools were crude. They were sharpened stones or bones sometimes attached to wooden handles. With the discovery of metals better tools soon followed. The first in about 5000 BC was copper. It was abundant and easy to work. It was malleable and ductile, but soft. It was improved by the addition of arsenic with difficulty, and finally bronze by the addition of 12% tin in about 4500 BC. But tin and copper did not occur near to each other. Enos implies that the need for tin encouraged early commerce in Europe. English tin was transported to Cyprus. The result was an ax or adz with a wooden handle. Bronze chisels offered significant improvement.
The discovery of charcoal allowed working metals at higher temperatures. That made processing iron practical around 1500 BC. Wood fires usually produce 400 to 600F. Pots fired in the ground could reach 1500F. Charcoal raised temperatures to 1800F. Glass was made by heating sand with a fluxing agent from wood ash or seaweed.
Blast furnaces produced cast iron which could be poured into sand molds to make useful items including pots, pans, fire places, etc. Pig iron could be forged into bar iron by heating red hot and pounding removing slag and increasing strength. Still higher temperatures and bellows blowing air into the melt made possible wrought iron with better properties. The drawknife was soon invented. And the saw. The first water powered saw mill is reported in 1594. Planes were used by the Romans but steel blades were better.
British war ships needed tall masts–over 100 ft. Availability in Britain was limited. American colonies had them but found transportation difficult. Iron processing required much charcoal. In Britain forests were denuded to provide for iron processing. The result was a shortage of firewood. Eventually coal was converted to coke, a suitable substitute.
Coal was abundant in Britain; it drove the industrial revolution there. Other countries including Germany and the US preferred wood. In Germany huge log rafts with up to 100 workers–up to 400 yards long and 90 yards wide–were floated down the Rhine to bring timber from the Black Forest. Softwoods were preferred because they floated and were easier to transport. Hardwoods like oak or cedar were used for durable structures like buildings, ships, and carts. Wood working was completed while the wood was green.
Netherlands had large peat deposits, a suitable fuel. Peat fueled early Dutch industries including saltworks, glassworks, breweries, dyers, potteries and brick works that provided red brick cities. When depleted they did not have coal slowing industrial development.
Clay soils could be baked to earthen ware pots or bricks by heating to 1800F. They were known as early as 4300 BC. Clay could be slapped over wicker walls to make them draft proof. Bricks could be reinforced with straw and left to dry in the sun.
The development of the wheel is discussed. The idea maybe arose from moving heavy objects on rolling logs. Stones for the pyramids or Stonehenge could have been rolled by attaching a frame that gave them a round surface.
Theoretically wheels could be sliced from logs but not until the arrival of saws. If cut in thin section they were likely to crack. Wheels in the Bronze age were made by joining two or three wood planks. They were heavy. Lighter spoke wheels began in 1500 BC in Egypt. The first paved roads are from 4000 BC. Most were corduroy roads made of split logs.
The potters wheel was known from about 3500 BC; the wood lathe about 1500 BC. In steam bending, wood is formed into a new shape which is retained on cooling. The method was known in the 18th century. Steam bending is used to make curved barrel staves. Wooden barrels were invented about 350 BC and were the shipping container of choice for eons.
The list of woodworking occupations is long. Carpenters, joiners, wrights, wheelwrights, shipwrights, wainwrights (makers of carts and wagons), bodgers (a turner who makes chairs of beech wood), bowyers, fletchers (made arrows), turners, bowlers, coopers, sawyers, foresters, colliers (made charcoal), and masons (made wooden handled tools). Users of wood included millers who worked in water mills and wind mills, and glaziers, potters, and smiths who used charcoal fires. Wood was an essential part of the Iron Age.
Musical instruments are made of carefully selected wood. Stradivarius violins used fine grained spruce harvested in the Alps.
In the Middle Ages thirty pounds of wood was needed to smelt one pound of iron. Wood was burned for cooking and heating. English woodlands produce two tons of wood per acre by the coppice method (compared to one ton per acre by replanting). In coppice, wood is trimmed to a stump and allowed to re-sprout. This produces wood faster because tall trees require years to develop a canopy and transporting water to the canopy is inefficient. England required 950 sq miles of woodland for firewood in the 1650s, about 1.6% of land area. Difficulty in the transportation of firewood limited the growth of cities.
Dry wood contains one half the energy of coal by weight, and is 40% as dense, resulting in about one fifth the energy per volume.
Ironworks used much charcoal and had to be located near iron ore and timber. In England, coal made Newcastle the fourth largest city by 1700. Shallow draft ships used to transport coal known as “colliers” were later used by Captain Cook in his explorations. In London people complained about the odor of burning coal as early as mid 16th century. London rebuilt with brick after the Great Fire of 1666.
The English economy–driven by coal fired industries–allowed intellectual development especially Oxford and Cambridge universities and the Royal Society. Robert Hooke is the first professional scientist. He was curator of experiments for the society. He promoted Joseph Moxon, who published Mechanick Exercises the first ‘how to’ manual for smithing, joinery, wood turning, bricklaying, and making sundials in 1703. Evelyn published Sylva, all that was known about trees, in 1664. In France, Diderot and d’Alambert’s Encyclopedie first appeared in sections beginning in 1751. Under Isaac Newton the society veered away from applied science to the work of the philosopher scientists. The need for water transportation resulted in canal mania in the second half of the 18th century.
Shortages of wood and charcoal in England drove up prices making English iron uncompetitive. Development of coke followed. Coke accommodated larger blast furnaces increasing productivity. In 1709, Abraham Darby learned to make coke by heating coal in a retort, a process similar to that used for charcoal. Darby made a fortune making cheap cast iron pots and pans. Darby’s process could use low sulfur coal–up to 2%, but high sulfur coal awaited development of the steam powered bellows and the addition of limestone to remove sulfur. Wood burning iron stoves soon followed. They were more efficient than open fires. Iron smelting with charcoal continued until the 1920s. Chemicals condensed from coal or wood retorts soon proved valuable raw materials.
Precision boring was a major new development. John Wilkinson used the method to make cast iron canons by boring solid castings. His method later made James Watt’s steam engine possible. The British fleet was equipped with cannons firing up to 32 lb cannon balls, as well as 16 and 8 pounders and smaller guns firing grapeshot and mortar shells. American steam engines continued to burn wood.
The nineteenth century brought the transition from wooden carriages and ships to iron, especially wrought iron. In the age of wood, bridges over 100 ft were rare, buildings were limited to six stories, and mills used wooden machinery. Cast iron proved unsuitable. Wrought iron was up to 3 times stronger in tension than wood and ten times as tough. The puddling process to make wrought iron was invented in 1783-4. A puddler could produce 220 lb of wrought iron in a day.
Suspension bridges made with wrought iron chains began in 1810. By 1864, wrought iron bridges up to 702 ft were in service. Buildings with wrought iron beams soon followed. The Crystal Palace of Britain’s Great Exhibition of 1851 was made of wrought iron. Wrought iron ships soon followed beginning with the Great Britain launched in 1843. Iron ships had better resistance to cannon balls and soon were preferred by the navy. The Statue of Liberty uses a wrought iron frame to support its copper panels. Rigging sailing ships required numerous pulleys. Wrought iron machinery was developed to mass produce them.
American railroads were built with wooden trestles. This kept costs low–$20 to 30K/mile vs $180K/mile in Europe. In Massachusetts machinery to make cheap cut nails was patented in 1795. Wire nails followed. Balloon framing was soon developed to make light wooden buildings. Screws were used as fasteners from the Middle Ages. Machinery to mass produce screws was developed in England in 1760. Pointed screws followed in the US in the 1840s.
Paper was traditionally made from discarded textiles. Production from wood pulp began in 1840 in Germany. By 1880s inexpensive wood pulp made daily newspapers possible. The improved kraft process followed.
The modern era featured the development of steel and concrete. Crucible steel was known from 1740 but was costly. The arrival of the Bessemer converter and the open hearth furnace made large scale production feasible. The Brooklyn Bridge was the first suspension bridge made with steel wire rather than wrought iron chains. Steel frames for skyscrapers began with the Home Insurance Building in Chicago in 1885.
Portland cement made by heating a mix of clay and limestone to 2500F was developed in the nineteenth century. The clinker is ground to a powder. It could be reinforced with steel to improve compression and tension strength. Prestressed concrete made by drilling holes in concrete and inserting wires under tension gives better properties. It is preferred for modern buildings and bridges.
The development of plastics is described beginning with Bakelite, a phenolic thermoset reinforced with wood flour. It was well established by the 1920s. Thermoplastics such as polyethylene and PVC developed after World War II. Composite plastics reinforced with fiberglass or carbon fiber are described as more recent developments.
Plywood made by gluing together veneer sheets were developed in the 1920s. Boats and airplanes were made with plywood in World War II. An array of “chip boards” are now made by gluing together wood materials of various sizes. Laminated wood beams made by gluing together sections of wood are also described.
Cellulose from wood or cotton fiber can be converted into valuable derivatives. The book describes rayon as “viscose.” It is a fiber made from cellulose. There is also “acetate,” cellulose triacetate, best known as safety film stock and nitrocellulose, aka guncotton, used as “nitrate” film stock. Cellophane an early clear packaging film is not described.
A chapter addresses myths. One is that construction of the Royal Navy destroyed Britain’s oak forests. Another is that deforestation results in soil erosion. Improved management methods–including coppicing–resolve these difficulties. In modern times, clear cutting forests and replanting with young trees raised in nurseries works better. Monocultural forests are more vulnerable to wind damage and to fungal diseases and pests. Ash trees are currently under attack. Previously diseases devastated chestnuts and elm. Tree farming has long lead times making it tough to know which trees will be most valued at harvest time. In Europe over mature oak forests resulted from the need to grow timber for shipbuilding–no longer needed.
Although titled as a book about wood, becomes an overview of materials technology. A selection of photos are included but the technical discussion would benefit from more illustrations. The book is British and does focus on European developments. US technology is included almost as a sidelight. That results in foreign terms like chip board and viscose. Ennos covers so much technology in short space it is no surprise that many details are omitted. Excellent references provide the interested reader with a path to more info. The plastics section covered in three pages is especially sparse and lacks references.
Readers will find this an informative introduction to many materials technologies. Reference, photos, index.