You will need the following lab supplies: INCREMENT CORE HOLDERS (shown right; cross-section in following panel), SCISSORS, RAZOR KNIFE, FINE MECHANICAL PENCIL (for marking holders), COTTON STRING (to apply clamping pressure during drying), DOWEL ROD (to remove cores from straws), and yellow woodworkers GLUE (to mount cores to holders).  Standard white Elmer's glue works fine too.

The increment core holders need to be prepared by a local woodworker equipped with a router table and 0.25-inch core box bit.  We typically use pine molding strips available in 12-foot lengths from a local building supply store.  Be careful not to route the groove to deep--50-65% of the core needs to remain proud of the surface for subsequent sanding.

Remove cores from their paper straws, and lay them into an increment core holder that has been pre-glued (do not be either stingy or excessive with the glue).  MAKE SURE THAT THE VESSELS ARE ALIGNED VERTICALLY IN THE SLOT.  Tightly wind the glued cores with cotton string (masking tape will also work) so as to apply pressure during the drying process.  When cores are dried, the string may be cut away with the razor knife.  Use the horizontal surface of the wood holder to record core identity and other information as you crossdate.

Use progressively finer grades of sandpaper wrapped around a wooden block to sand down a flat surface on the core.  If working by hand, begin with the coarsest 100-grit to get to a flat surface, then polish it to at least 320.  If you have a belt sander available, you can start with a 240 grit belt (but go easy, the wood comes off quickly) to make the intial surface before moving to finer hand sanding.  The smoother and cleaner you get the surface, the better the wood features can be observed.  Most woods will actually require 400-1200 grit paper, but the latter can be hard to find.

Shown here is a freshly finished White Pine (Pinus strobus) increment core (finished to 400 grit) mounted in its holder.  Note that the annual rings are now clearly visible as are the individual resin ducts (brown dots).

Shown here is the first step of crossdating.  Under a good dissecting microscope, begin counting backwards from the first known year behind the bark.  Using a fine mechanical pencil, place a single dot on each decadal ring (e.g., 1990, 1980, 1970, etc.), place two dots on each 50-year ring (1950, 1850, etc.), and three dots on each century ring (1900, 1800, 1700, etc.).  At this stage, these marks are just temporary year assignments.  The actual years will be confirmed after skeleton plotting.

This is a skeleton plot for a 30-yr-old tree core.  They are typically graphed on mm graph paper (available at most office supply stores).  The particular tree on which this plot was produced was cored in late 1996, so the last ring was complete and is designated as the first ring behind the bark.  The decades are labeled on the x-axis and a vertical line is drawn on a y-scale composed of 10 units.  Any ring that is smaller than its neighbor rings (± 3 on either side) gets a line drawn on the paper.  If the ring is very small, the line may be 10 units. If the ring is half as small as its predecessor you might code it as a 5, etc. (rings that are coded less than a 5 are rarely useful in crossdating).  This is a bit counterintuitive because the longer the line, the smaller the ring.  From this example, we see that there are a pair of rings (1980, 1981) that show up as exceptionally small.  We can now confirm the presence and date of this pair of rings in each increment core from our total sample.

Once you have finished crossdating, you may find that you need to shift your pencil marks in one direction or the other to accommodate the cross-validated information.  Once you have finished with this process you now have exact years on every core.  The pencil marks should now be made permanent by using a probe to put pricks in the wood (these will not smudge out with further handling like pencil will).

Equip yourself with a dissecting microscope and adequate light source.  For the purposes of our introductory laboratory, we can measure individual tree rings to the nearest 0.1 mm using the process of interpolation.  NOTE that when conducting research-grade studies, a sliding electro-mechanical stage is usually employed that records rings widths to the nearest 0.01-0.001 mm.

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A small plastic ruler (marked in mm) is held up to the base of the core.  Based on this configuration, the center of the tree is to the right and measurements should be made from right to left.  Visually, you line up the beginning of the earlywood (right red line) and measure out to the end of the latewood (left red line).  There is no sub-markings between the third and fourth mm, therefore, visually break this area up in to tenths.  Thus, we would estimate this ring width as 3.1 or 3.2 mm.  NOTE that plastic rulers with inked markings are often inaccurate--a stamped metal machinist's rule would be much better if available.  Record the ring width to the nearest 0.1 mm for every ring in each core.