The following is an extract from my book Dress and Identity in Iron Age Britain: a study of  glass beads and other objects of personal adornment published by Archaeopress (ISBN: 9781784915261). It is a guide that I put together on how to measure and describe glass beads, but particularly those from the Iron Age.  

If you use the information from this blog post in something you write, please cite it as: Foulds, E.M. 2017. Dress and Identity in Iron Age Britain: a study of  glass beads and other objects of personal adornment. Oxford: Archaeopress, 247-53. 

Appendix A

Terminology & Guide to Recording Glass Beads

The quality of the descriptions of glass beads varies between archaeology reports and the typologies designed by Guido (1978a), Stead (1979), Dent (1984), and Gray (Bulleid & Gray 1966). Therefore, for comparability, consistency and clarification it became necessary to define a number of terms. The necessary terminology concerns the description of the physical appearance of the beads, namely: size, shape, colour, and decoration.

Glass beads dating to the Iron Age are often very simple in their nature compared to other time periods and cultures, but they do require a specialised and standardised vocabulary for describing them. Iron Age beads could exhibit an unlimited number of characteristics; however, their one key aspect is that they have a single central perforation that allows the object to be strung. Although similar types of objects with multiple perforations (i.e. ‘spacer beads’) existed in previous periods, such as on Bronze Age jet necklaces, there is no evidence for their use in the Iron Age. If they were used, then they were likely made from organic material that has not preserved. Beads with off-centre perforations are considered to be pendants and to date have also not been found in Iron Age contexts. Caution is also needed when classifying an object as a bead, as beads and spindle whorls can sometimes be confused (Liu 1978). Both of these objects can be very small and have a centrally located perforation and it can serve as both a bead and spindle whorl at different times. Context of deposition would be the ideal method for distinguishing between whorls and beads, but as has been shown in this research, unless the deposition was made in an inhumation, the feature gives very little indication as to how the object was used.

Dimensions & Shape

Description of the size of glass beads is based on three primary measurements (Figure 182). As the majority of glass beads from the Iron Age were round when viewed from the perforated end, Diameter is used to describe the line that passes through the perforation. In some examples, beads are not perfectly round or they may have had intentional decorative protrusions. In these cases, the maximum diameter was recorded. For beads that were not round when viewed from the perforation end, Length and Width measurements were taken through the perforation. In order to make this measurement comparable throughout the study, the larger of length and width was compared with bead diameters.

The second measurement, Height, refers to the length from one end of the perforation to the other end. Together, diameter and height express the overall size of each bead. Just as the overall size of each bead varied, so too did the size of the perforation. This reflects both the size of the mandrel that the bead was formed on, and the maximum size of the material that could be used to string each bead onto. This measurement is referred to as Perforation Diameter.

Closely related to dimensional data is bead shape. The terminology used here largely follows the terms used by Guido, although she did not explicitly define them. It is essential to define them here, as they are used throughout (Figure 183). Others (especially Beck 1928), have used shape in conjunction with a Diameter:Height ratio of bead measurements. For example, a perfect sphere would have a 1:1 ratio. A modern 1 pence coin would have a 20.35:1.67 ratio or could be described as 12.19, meaning that the diameter is much larger than the height and is therefore disc shaped. What this describes is the relative diameter compared to the height. Thus all round beads with a value of 1 would be perfectly spherical, while a round bead with a ratio value of 2 would be roughly disc shaped. Beck (1928) used these ratios in his universal approach to classifying bead shape. This comprehensive guide divided beads into Long, Standard, Short, and Disc beads according to their Diameter:Height ratio.

This differentiation in shape for round beads is largely followed throughout the analyses, but with some modification (Figure 184). Round bead shape terms are termed barrel, globular, and annular. This approach has been especially useful as beads between about 1.4 and 1.7 are often difficult to differentiate between globular and annular beads with these proportions. However, it is recognised that these definitions are completely arbitrary and may not reflect the shape types used by the Iron Age glassworker (see Figure 21 and Figure 51). One might expect that there would be clear distinctions between beads of more spherical shape and those that are more disc-like in shape. However, as the analyses showed in Chapter 6, this is not the case. Instead, beads described as globular and annular form a continuous spread between the boundaries of both descriptions. This suggests that the rules for creating bead shapes were not clearly defined. Instead of thinking of these shape terms as permanent and unbending, especially for globular, annular, and barrel beads, it is better to think of them as towards one end of the spectrum or another.

The majority of linear measurements were taken first- hand using a set of plastic digital calipers. On some fragmented beads, particularly those where less than 50%  remained, the diameter could be estimated. As a digital photograph of each bead was taken with a scale bar at the time of analysis, measurements of fragmented beads could be estimated with the aid of computer software. ImageJ (available for free: http://imagej.nih.gov/ij/) was used for this purpose and tests that were conducted have shown that this is a fairly accurate method for measuring glass beads.

In addition to bead dimensions, the weight of each bead was recorded where possible (i.e. when not mounted permanently onto a display board, or strung together for display). This was accomplished with a standard digital pocket scale.

Colour & Decorative Motif

Providing a description of colour was perhaps one of the most challenging aspects of discussing glass beads. Such a description is made up in part by the hue, but can be affected by the degree of translucency. For example, shining light through a very translucent piece of glass can affect the perception of its colour. In glass, both colour and opacity are manipulated through the addition of minerals or metal-oxides. Natural glass, or glass that has not been altered, will often appear as a pale translucent green due to iron impurities in the silica (Henderson 2000, 27). It is sometimes referred to as bottle-glass, although this should not be confused with colourless glass that has been decolourised through the use of additives.

In other literature about glass, discussions regarding colour are often restricted to their chemical composition obtained through the use of analytical techniques, such as XRF or SEM (e.g. Arletti, Vezzalini et al. 2008; Foster & Jackson 2009; Henderson 1982; Linden, Cosyns et al. 2009). However, chemical analysis was not a goal of this research project, as it does not describe the way in which a colour was used in combination with other colours. Nor does it aid in our exploration as to how the glass was used or provide data on the wider archaeological context. Colour can also be measured through the use of equipment, such as a spectrophotometer. The pilot study phase of this project tested the applicability of such equipment with glass beads. Unfortunately, this method was deemed unsuitable for this purpose, because the application of colour on these beads often occurs as very thin threads or small dots, which were too small for analysis. This made it impossible to apply this type of approach to all types of Iron Age glass beads, thus making it difficult to gather data for a statistically representative sample.

Due to the difficulties of describing colour in a non- subjective manner, this study relied on the observations made by the author during first-hand analysis. In many cases this allowed the published descriptions to be confirmed or elaborated where necessary. As a record of observations, the digital photographs were taken with a colour scale bar to help ensure that the photographs were taken under similar lighting conditions, and thus not distorted by lighting. It also allows for material held in different museums to be compared later, as for example the beads from the Queen’s Barrow from Arras, East Yorkshire are split between the Yorkshire Museum and the British Museum. In cases where glass beads could not be viewed for the thesis, written descriptions had to be relied upon.

Each description of a colour found on an Iron Age glass bead should include the hue, whether it is translucent or opaque, and in what sense it was used on the bead. For example DB 16364 (Figure 189m) would be described as: translucent green. As a second example, DB 4316 (Figure 189x) bead would be described as: opaque yellow. Both of these examples are monochrome, so the colour refers to the body of the bead.

Guido identified 16 different motifs in her discussion of glass bead appearance (Figure 3 [not shown here]). However, her descriptions and accompanying images left out a number of motifs and do not correctly demonstrate how the motifs are used on glass beads. As one of the attributes of physical appearance that was analysed during the research, it is necessary to define the different motifs that were found on the beads (Figure 185).

For the majority of these beads, a decorated bead was created by applying decorative elements to a monochrome bead with a contrasting colour of glass (Figure 186). This decoration is seen on beads with eye motifs, and linear designs, such as circumferential lines or zig-zags/wave motifs. For other motifs, the design is actually integral to the bead form, such as the wrapped or whirl beads (as in Figure 185). Some of the decorative motifs are continuous, such as the waves and whirls that completely encircle the bead. Others beads are made up of multiple instances of each motif. For example, motifs such as eyes and spirals always occur at least three times on the surface of the bead. The placement on the surface of the bead usually follows three main patterns (Figure 187). A full description of each motif can be found in Figure 188.

Other Aspects

There are a few other characteristics of glass beads that are worth recording and reporting

on. In addition to measuring the perforation size, as mentioned above, the shape of the perforation should be recorded. Not all perforations are circular, as some are oval and even square. Perforations can also be described as ‘tapering’, where one is larger than the other, or they can be described a ‘straight’, where they are equal in size. This most likely relates to the shape of the mandrel used to make the bead on. Glass beads made on a mandrel are not likely to be ‘hourglass’ shaped, like some stone beads, due to the methods of manufacture.

The current state of the bead should also be recorded. For example, an approximation of the percent present, the degree of

weathering, and whether any secondary modifications are present. It is not unusual for Iron Age glass beads to be found whole, as much of the glass of this period appears to be very long lasting and unbroken. When they are broken, it is usually half a bead that remains although smaller pieces are also sometimes found. A few examples exhibit evidence of secondary modification (e.g. DB 11630 in Figure 191v), which should be recorded. Finally, the degree of weathering that is visible on the surface should be assessed. Brill (1999) provides a good method of assessment of weathering stages.

Photographing Glass Beads

High quality photographs are essential, not only for recording the condition and appearance of glass beads, but also to be transparent about the terminology used and to be able to make comparisons based on photographs alone. A good photograph should be well composed, lit, and there should be consistency in the way beads are presented. Ideally, the camera should be affixed to a tri-pod and shutter release cable to ensure that the user does not cause blurriness to the photograph. A spirit level should be used to ensure that the camera is square with the table. This is especially important, as it ensures that if the images are used for analytical purposes, that any measurements will be accurate.

The background and composure of a picture should be as consistent as possible. As Iron Age glass beads can be both very lightly coloured and very dark, I used a light gray photographic background to photograph them on. A black background is heavily advised against, as many of the beads are very dark. I did not use any special lighting when photographing beads, as facilities and study space at museums were variable. Instead, I used the light that was available. Ideally, the bead should be evenly lit, so details are not obscured. I used a scale bar with a colour scale to ensure that when the digital photographs were processed, images could be corrected were necessary.

Assuming the bead is complete, photographs should be taken of both perforation ends, as well as a profile view. In many cases, as beads can be irregularly shaped and decoration can extend to the non-viewable side, many photographs should be taken of the profile as the bead is rotated. This means that the entire pattern is captured. In addition to these photos, further photos may be needed to capture specific details, such as interesting or unusual features, breakage, evidence of wear, or secondary modificiation. This may include photos where the bead is positioned so that it is oblique, especially for details of the perforation hole. For consistency, fragmented beads should be photographed in the same manner for comparison with complete beads.

Due to the round and/or odd-shaped nature of glass beads (or in the case of broken beads), at least one of these views may be difficult without the bead rolling around. I took a small plastic box of white sand with me, which was used as the sand helps prop up the object when taking photographs. The box I used was also large enough for a photographic scale to be included. If at least part of one perforation end remains, it is important to take a picture of the bead squarely set into the sand box (with scale bar), so that software can be used to estimate the original diameter. I experimented with the use of a light box for illuminating transparent glass beads, which had mixed success. Often, the light was not strong enough to pass through some of the deepest glass. I found that a powerful LED torch had better success.

Chronology Terminology

One of the difficulties in comparing evidence for different areas of Britain during the Iron Age is in the terminology used to discuss chronology. As change through time is tracked by changes in settlement, artefacts, and practices for the treatment of the dead, this can be very regional (e.g. Harding 2004; Moore 2006b). Therefore, a common terminology is needed in order to discuss periods throughout Britain. Here, I have borrowed from Hill’s (1995a) periodisation from his overview of the Iron Age in Britain:

• Early Iron Age: c. 800 – 450 BC
• Middle Iron Age: c. 450 – 100 BC
• Late Iron Age: c. 100 BC – AD 43
• Early Roman: c. 1st century AD
• Romano-British: c. end 1st century AD+

In term of the transition to the Roman period, I have used ‘Early Roman’ and ‘Romano-British’ purely as a short hand method for referring to a date range, rather than the effect of romanisation or level of interaction with the Romans. As it can be particularly difficult to separate out Late Iron Age and Early Roman period activity and these periods overlap, depending on the archaeological evidence for dating, in some cases these periods are combined and in other cases they are left separate.

Works cite

Arletti, R., G. Vezzalini, S. Quartieri, D. Ferrari, M. Merlini & M. Cotte, 2008. Polychrome Glass from Etruscan Sites: First Non-Destructive Characterization with Synchrotron Μ-XRF, Μ-Xanes and Xrpd. Applied Physics A: Material Science & Processing, 92, 127-35.

Bulleid, A. & H. Gray, 1966. The Meare Lake Village, Volume 3, Taunton: Taunton Castle.

Stead, I. M., 1979. The Arras Culture, York: The Yorkshire Philosophical Society.