Saturday, January 9, 2010

Ferreting Out the Ferrous

Ah, metal detecting, a favorite pastime for beach combers and airport security guards. We use a portable metal detector to find metal artifacts during project area surveys. Each “mag hit” is flagged, numbered, and mapped. Artifacts recovered are labeled with the corresponding location.

The sensitivity of a metal detector can be adjusted to find objects of a certain material or at a certain depth. A tone sounds when metal is detected. The pitch of the tone indicates what kind of metal it is. With practice, a metal 'detective' can learn to discern the differing tones and bypass modern trash. While the accuracy isn’t 100%, it is an additional tool in our arsenal to help us learn all we can about a site.

Friday, January 8, 2010

Screen it!

Once you have shoveled and troweled, what are you going to do with all that soil? Why, screen it of course! An archaeological investigation is not possible without the use of a screen for sifting away soil to find artifacts. Screens can vary in two main ways: set-up, and size of the mesh.

How the size of the mesh can change is self-explanatory...either the mesh is made up of smaller holes or larger ones, depending on the site and what materials the excavator is looking to investigate. We use a quarter-inch mesh, which is perfect for catching little bits of glass and ceramic, while letting the really, really tiny pieces pass through the screen. Of course, this mesh can also be made of different grades of material, though the stronger mesh is best for extending the life of a screen. There is more variety in the types of screen available, some of which are the free-standing screen, the tri-pod screen, the hand-held screen, the nested screen, and the H-frame. It is possible that you know these screen by different names, but these are the most basic for describing them.

Free-standing or Lavish screens are most people's favorite, except when it comes to being mobile. If you have worked with us down at Port Tobacco, you have had the privilege of using one of the lovely Lavish screens made by Dan Coates. While these are very comfortable to use with multiple people, are lighter than many free-standing screens, and can screen large quantities of soil faster, it is still a bit difficult for one person to lug one across longer distances, and is too bulky for shovel testing (especially when testing in a densely wooded area). Nevertheless, this is definitely one of the easiest screens to use, requiring little effort on the part of the screener.

Tri-pod screens (image to the left) have also been used down at Port Tobacco, and are exactly what they sound like--a screen in a wooden frame suspended by a rope from three rods that form a tri-pod. These require a little more effort than the Lavish screens since you are in charge of shaking the soil rather than having the assistance of wheels and a track, but these screens are conveniently collapsible able for travel. Hand-held screens (image to the right) are just the wooden frame with the wire mesh, and, due to their smaller size, are perfect for sites that need to be hiked into...however, you do have to support the screen while shaking it, and with a heavier clay soil I imagine this can get quite tiring. These screens also are unable to screen large quantities of soil quickly due to their smaller size.

Nested screen (at left) are generally used for finding very small materials. The screens vary in sizes (measured in millimeters) and rest on top of one another. When shaken, the largest material remains on the top screen while everything smaller than the size of the mesh falls through to a second screen which has smaller holes, once again allowing smaller materials to pass through while stopping anything larger than that particular mesh size. Three or four sizes can be stacked on one another, and are tedious to use but excellent for recovering tiny artifacts such as fish scales or very small beads like the one in yesterday's blog.

It is likely that many of you have also used an H-frame screen (image to the right), our screen of choice when out excavating shovel-test pits. This screen rests on two legs and is held up by two handles the screener holds and used to shake the screen. These are perfect for a site that requires mobility, as a person can carry one or two without much difficulty. These screens also fold flat, making it quite easy to fit several of them into Jim's truck.

A tarp can also be used in conjunction with these screens to aid in backfilling, though they are best for filling in shovel-test pits.

So, when searching for artifacts in soil, choose your weapon and just screen it!


Thursday, January 7, 2010

Through the Looking Glass

When artifacts come in from the field, we use various tools to process and analyze them.
Microscopes are useful for looking at fragmented or very small artifacts, such as seed beads, inclusions in ceramics, and lithics. We can also look at the composition of soils and stones. Here at the lab we have a binocular scope (top) and a digital microscope (left). The binocular scope has two eyepieces, or oculars, through which the object on the slide is viewed. It can magnify objects to 4x, 10x, 40x, and 100x.

The digital scope is hooked up to a computer and the object is viewed on the screen. The magnification options are 10x, 60x, and 200x. It can take digital photos of the artifacts as well. This purple glass bead (below) has a diameter of 3 millimeters. This picture was taken with the digital microscope at 10x.

Microscopes are certainly not unique to archaeology, but they are essential for thorough lab work.

Click on any of the images for a larger view.


Image sources: and

Tuesday, January 5, 2010

To trowel or not to trowel...

A trowel is to an archaeologist as a pen is to a writer--an absolutely necessary tool for work. I am certain that many of our loyal readers are familiar with the trowel, whether having used it to remove soil in a unit, its principal use, or to sort through materials in a screen. A trowel is used for excavating different strata in a unit, and is especially helpful for defining the edges of a feature (especially when there is a color difference visible in the soils) or gently removing one stratum to reveal another. In your archaeology travels you have likely happened upon two different types of trowels.

The first type has a pointed blade (see image to the right), and in the masonry world would be known as a bricklayer's trowel. These trowels are generally used for spreading or shaping materials such as mortar or plaster. For concrete construction, a rectangular finishing or margin trowel (see the image below) is usually used for smoothing or texturing the concrete. Both of these trowels are flat on the bottom, which is necessary in archaeology to avoid accidentally digging into a different stratum. There are many other types of trowels both big and small, but the two most commonly adopted by archaeologists are the pointed type and squared off type. Why two different types of trowels? Well, pointed trowels are generally used on prehistoric sites while the square trowels are better suited for historic sites. So, if you are a historical archaeologist you had better be carrying a square trowel in your back pocket...that is just the way things are.

Just kidding folks! Neither type of trowel is better for one type of a site over another. Rather, it depends on the soil and materials being excavated. As such, it is not unheard of to use a pointed trowel at a historic site or vice versa...actually, it is not even taboo or strange, despite what you may hear out in the field. I personally prefer a pointed trowel as it is what I first learned to use, though that is not to say I cannot pick up a square trowel is the situation warrants it! I find a square trowel especially handy when cleaning up a wall or corner of a unit.

Also, next time you are out in the field not only note the types of trowels and their uses, but remember to sharpen the edge of your trowel for a much easier and cleaner job!


Tools of the Trade

As we have been taking a break from Port Tobacco to attend to other projects, the blog this week will not be highlighting any particular artifacts or information directly related to the site. We will be delving into Port Tobacco material again as we begin working on the report for the sites included in the Preserve America grant (the Swann house, the area April and her students worked on over the summer, and the Union encampment site. Be sure to keep an eye on the blog for posts on our progress and any interesting finds. Until then, I present you with...Tools of the Trade, a segment on the tools we use in the field of archaeology! Surely you have seen or used these tools down at Port Tobacco, as well as at other archaeological sites you have worked on. Today I bring you the shovel and the spade!

While a trowel may be the first tool that comes to mind when considering the fine detail work in the field, most sites require the use of a trusty shovel long before you begin to trowel. A shovel is a crucial companion when digging shovel test pits, and also comes in handy when moving large amounts of dirt out of a test unit.

In the field, it is important to make sure you call a shovel a shovel and a spade a spade. When we refer to a shovel, we are referring to that common tool with a pointed end and a slightly curved blade (see the image to the left). These are excellent for excavating shovel test pits, removing large quantities of soil from a unit, working in gravelly soils, and splitting those obnoxious roots that cut across a unit. A spade differs from a shovel in that it is flat, enabling you to create a unit with a nice straight wall. A spade (see the image to the right) may not be the best for lifting and moving soil, but they are excellent when working in a test unit as their flat edge prevents you from digging unevenly, which can mix different strata. Of course, both shovels and spades come in different lengths and sizes, which is important when considering what type of work you are going to be doing.

So, next time you are out in the field you should know whether you need to reach for a shovel or a spade (that is, if you did not know already!)


Monday, January 4, 2010

Happy New Year

There were no comments or guesses on last week's Guess the Artifact. I'm sure faithful followers were just consumed, like we were, with the holiday chaos and resulting urge to sleep for a very long time.

Now its a brand New Year and we can return to normalcy.

Last week's Mystery Artifact was...Fire-Cracked Rock!
Don't let the lowly name fool you; FCR is an important indicator on Prehistoric sites. In the Mid-Atlantic region, FCR is usually quartz or quartzite. The photo in last weeks blog was quartzite FCR. These lithics are created when the stones used in a fire pit or hearth were split and/or reddened by the heat. FCR breaks are angular and often have several faces.

And now for this week's Mystery Artifact(s):


Obviously these are nails, but there are three different types of nails. Can you guess which nail is which type?