Tuesday

Raven pins four strips of paper to the Bench: Wood, Oil, Sand, Ore. "Each one is a starting line," she says.

Rocket slaps a paper towel under Wood. "Trees to chips to mush to sheets. I read ahead."

"Mush has a name," Raven says. "Pulp. What do you notice about how the fibers come apart?"

"Chemicals cook the glue away," Rocket says. "Or a grinder tears them apart. Two ways."

Nova hovers over the Sand strip. "This one needs a lot of heat," she hints. "More than any kitchen can make."

"Sixteen hundred degrees," Rocket reads. "Quartz melts and cools into glass. That is not a Bench job."

Raven laughs. "Nothing today is a Bench job. Today we read."

You need fiber to make paper. Today the fiber comes mainly from two sources: wood and recycled paper.

Wood chips, from logs or sawmill leftovers, are separated into individual wood fibers. This process is called pulping, and pulp is a mix of cellulose fibers and water.

Chemical pulping is the most common kind in the United States. The chips are cooked under pressure with chemicals that dissolve the lignin, the glue that binds the fibers.

In mechanical pulping, chips are pressed against a grinder that tears the fibers apart. These fibers are shorter and make weaker paper, such as newsprint.

The watery pulp is pumped onto moving wire screens. Water drains out and the fibers interlock into a sheet. Rollers press out water and steam-heated drums dry it.

The petrochemical industry uses petroleum as a raw material, called a feedstock, to make plastics and hundreds of other products. Natural gas is also used as a feedstock.

A plastic is mostly polymer. A polymer is a large molecule formed from many smaller molecules, called monomers, bonded in a repeating pattern.

Under the right conditions, molecules of ethene join end to end into the polymer polyethylene. Hundreds or thousands of monomers can link into one chain.

Different forms of polyethylene make plastic bottles, plastic bags and harder objects such as crates. Polypropylene is stiffer and goes into plastic utensils.

Not every polymer is synthetic. Rubber is a polymer made naturally by rubber trees.

Silicon makes up nearly one fourth of the mass of the earth's crust, second only to oxygen. Quartz is the usual crystal form of silicon dioxide: hard, brittle, clear and colorless.

High-silica sands are the sands used in glassmaking. At 1600 degrees Celsius, quartz melts into a thick liquid. When it cools, it does not form crystals. It forms glass.

A glass is a solid without a regular repeating structure. Silica glass is highly transparent, and sudden temperature changes do not crack it easily.

Iron ore is rock made almost always of iron oxides. Heated together with a helper substance called a reductant, it yields metallic iron.

Steel is a combination of iron with a small amount of carbon. Almost all iron ore, about 98 percent, is used in steelmaking. Steel is shaped by casting, forging and rolling.

Four journeys traced. Tomorrow is Bench Lab: you will test the materials themselves and match each property to a job.