Pithwell

Count back from the bark.

Pithwell dates old timber by its tree rings. The outermost ring is the year the tree was felled; every ring inside it is one year earlier. Scroll, and this section is read the way we would read it: newest ring first, down to the pith.

Ring number, counted from the pith. The frame holds up to 43 rings; 38 lie along the marked line.

Scroll to read inward

Ask about a sampleHow crossdating works
A tree trunk cut straight across and photographed head-on: about forty fine concentric growth rings in orange wood around a small dark pith, with stained, darker wood in the corners.
Newest woodThe outermost rings in this frame.
One ringPale earlywood, then a dark band of latewood.
A fine crackIt runs along one ring.
PithThe first year’s wood. Everything else grew around it.
Method

How can a ring give you a calendar year?

A tree adds one ring a year, and its width follows the weather. Many trees in one region share the same run of wide and narrow rings, so an undated timber can be matched against dated ones. The match fixes each ring to a calendar year; with the bark edge intact, the last ring is the felling year.

In a softwood like the one pictured, each ring is a pair of bands. Earlywood grows in spring and is pale, with wide, thin-walled cells. Latewood grows later in the season and is darker, denser and narrower. The sharp edge between one year’s latewood and the next year’s earlywood is the line that gets counted.

Width is the signal. A warm, wet summer lets a tree lay down a wide ring; a drought or a late frost leaves a narrow one. Trees in one region get the same weather, so their narrow and wide rings fall in the same years. Matching those patterns between samples is called crossdating, and it is the whole method. Chronologies built this way now run past 12,000 years.

MASTERdatedSAMPLE AundatedSAMPLE Bundated18011810182018301840
Starts in 1810: 5 of its 6 narrow rings line up.
Illustration with invented widths, not measured wood. Slide sample A until its narrow rings fall under the master’s: started in 1810, 5 of its 6 line up. Sample B, at the same shift, manages 1 of 7.

The photograph on this page holds no date, so we can count its rings but not name their years. We counted 38 along the line from the pith to the top edge of the frame, with software that follows each ring outward, and checked the count against a second method. On the four cleanest rays the two agreed to within one ring.

A close crop of the wood: horizontal bands of pale, crumbly earlywood alternating with narrower, darker, denser bands of latewood. Six complete rings are visible.
Six rings at full detail: a 720 × 480 pixel crop of the original 5,381-pixel photograph. Pale, crumbly bands are earlywood; the dark, dense bands are latewood.
What a sample needs

What does a timber have to show before it can be dated?

It needs a long enough run of rings to match, and ideally the bark edge. With the bark edge, the last ring gives the felling year. With some sapwood left, we can give a range. With none, the result is only a date after which the tree was felled. We say which of the three you have.

160016101620163016401650166016701680BARK EDGElast ring 1647SOME SAPWOODlast ring 1624HEARTWOOD ONLYlast ring 1610FELLED 1647FELLED 1633 TO 1665last ring + 9 to 41 sapwood ringsFELLED AFTER 1619last ring + at least 9 sapwood rings
The three kinds of result, drawn with invented dates. The nine-to-41 range is a published sapwood estimate for medieval and modern English oak at 95% confidence; real estimates depend on region and period.
In words
The bark edgeThe felling year, from the last ring. If that ring is incomplete, often the season of felling too.
Part of the sapwoodA range for the felling date. Published sapwood estimates for English oak run from about 9 to 46 rings, depending on region and period.
Heartwood onlyA “felled after” date: the last ring plus the minimum sapwood allowance. The real felling can be decades later.

A long run of rings matches with more confidence than a short one. Reports from English Heritage’s Ancient Monuments Laboratory, held by the Archaeology Data Service, caution against relying on a single timber with fewer than 100 rings. The timber page goes through what a result states.

Material

What kinds of wood can be dated?

Any wood with clear annual rings, from a species and region that has a reference chronology. That covers roof and floor timbers, oak panels and chests, ship timbers and the spruce tops of violins. Tropical woods without clear annual rings, and species with no regional reference, are much harder.

  • Roof and floor timbersOften several from one building, which gives a firmer date.
  • Oak panels and chestsThe surface is often the only edge there is to read.
  • Ship timbersLarge pieces can carry long runs of rings.
  • Violin topsSpruce with narrow, even rings that suit measuring.

Reference records are public. NOAA’s International Tree-Ring Data Bank holds ring-width, density and isotope records from more than 5,000 sites on six continents. A chronology only helps for the species and the region it covers, so the first question about any sample is where the tree grew. We would rather give a plain “cannot be dated” than a date that does not hold.

Four more questions

Does tree-ring dating damage the timber?
Usually very little. Where a cut end is exposed, the surface can be sanded and read in place. Otherwise a small core is taken: hand borers for living trees take cores about 5 millimetres across, and the tree normally seals the hole. For a carved or painted object we would first ask whether an exposed edge already exists.
Why do you count from the bark inward?
The bark edge is the one ring with a known year: the last the tree grew. Each ring inside it is one year earlier, so counting back from it keeps every date anchored. Reference chronologies are built the same way, from living trees back through older and older timber that overlaps them.
How far back can tree-ring dating reach?
Some regional chronologies run back more than 12,000 years, built by overlapping living trees, dead trees and timber from buildings. Whether your sample can use one depends on its species and where it grew. No single chronology covers every wood or every place, so some timbers cannot be dated at all.
Can you tell a tree’s age from a stump?
Counting rings on a stump gives the tree’s age at that height. It falls a few years short of the true age, because the sapling needed time to grow that tall. A core taken nearer the ground gets closer. Neither gives a calendar date unless the rings are also matched against dated wood.
A narrow strip of the outer rings of the same wood, laid flat like a core sample.

Ask about a sample

Tell us what the timber is, where it came from and whether any bark edge or pale sapwood survives. A photograph of the cut end, with a ruler beside it, is the best first step.

Ask about a sample
Sources

Where the facts come from