A Further Analysis of the Fiber Coats of the Icelandic Breed of Sheep

by Margaret Flowers

It’s well known that the fleece of the Icelandic Breed of Sheep is dual-coated, consisting of a coarse, long waterproof tog and a fine insulating thel. Analysis beyond these bare facts has been slim; Abbott (2001) reported that the weight of the tog is approximately 50% of the total weight, and mentioned that the tog is actually comprised of multiple layers. These layers can be separated by hand, and also by equipment in commercial mills; however, only hand separation renders all layers capable of further use. While the contribution of each layer to the mass (weight) of a sample of fleece can be readily ascertained with a sensitive enough balance, the contribution of the number of fibers in each layer and the micron profile of each layer has not been previously determined. This information has practical implications for the best end uses of the fleece.

**Intact and separated locks of Icelandic sheep**

Coat analysis: how heavy and how many?

Duplicate samples (10 cm x 10 cm) of fall fleece from two unrelated Icelandic sheep, Dryngja (DL 247B) and Hamra (BEL 736C) were removed at skin level at the mid-side location recommended for micron analysis in October, 2017. These four samples (Dryngja A and B and Hamra A and B) were each carefully separated by hand into the component coats: thel, inner tog, intermediate tog, and outer tog. Each coat sample was weighed and the percentage of the total was determined.

Five replicate sub-samples of 30 fibers from each coat of each of the four samples (this number was experimentally determined to produce accurate and repeatable results) were weighed on an analytical balance to an accuracy of 0.1 mg. The values of the replicates were averaged, and the mass per fiber determined for each of the coat samples. The number of fibers in each of the coat samples was estimated (using the value of the total mass of the sample layer), and the percentage of the number of fibers in each of the sample coats was calculated, based on the total mass of the fleece sample. The accuracy of the estimated numbers obtained by this method was verified by actual counts of the three tog layers of Dryngja A; the percent error was less than 4% for any sample. The number of thel fibers in the samples were too great to do an actual count.

The results for both mass and fiber number in the separated coats for each sample of Dryngja’s fleece proved to be very similar, so these were averaged. The same was true for Hamra’s. It was also apparent that there was also great similarity between the two sheep as can be seen in both the mass and fiber numbers of the individual coats. For both, the thel weight was approximately 50%, as reported by Abbott (2001).

Coat analysis: how fine and how much?

To visually represent the contribution of each of the layers to the fleece of the Icelandic sheep, duplicate fleece samples contiguous to the ones used in the above study were taken and sent to Yocom-McColl Testing Laboratory, Inc., for micron analysis. Two complete samples for each sheep were analyzed, as well as samples of separated thel, inner tog, intermediate tog, and outer tog. The numerical results were then applied to the histograms of micron diameter provided by Yocom-McColl to visually represent the contribution of each of the layers to the fleece of the Icelandic sheep. Because of the similarity of the numerical results and of the micron results, Dryngja was selected as the model for visual/ graphical representation of the fiber coats.

The results from the micron fiber analysis are presented as a histogram of the percent of fibers at each fiber width (recorded in microns). Below are the histograms of a complete sample of Dryngja, and the histogram of the outer tog. Note that there is a difference in scale; the percent of observations (y- axis) is of the fiber sample. Hence, the very low peak above 32 μm (= outer tog) in the entire fleece sample (Dryngja 2) appears greatly enlarged when only those fibers are tested (Tog 3 = outer tog). Since these were different (but contiguous) fleece samples, the shape of the peak is not identical.

One of two complete samples of Dryngja and the outer tog sample (tog 3) analyzed by Yocom-McColl Testing Laboratories, Inc. Note scale difference.

Additional information provided by Yokom-McColl are the average fiber diameter and the percent of fibers greater than 30 microns. This is also useful information in determining the best use of the fleece from which the fiber was taken.

Note that the fiber diameter of the thel sample is recorded as higher than that of the complete sample, which includes all tog layers as well as thel. There are several factors that could account for this. First, the complete and thel results were not measuring the same sample, but contiguous ones: one that was untouched, and one that had the tog fibers removed. In addition, the tog removal was done mechanically (by hand) by removing the longest, coarsest tog, followed by shorter and finer tog layers. What remained was the “thel”, which might easily have contained coarser fibers that had not yet exceeded the length of the thel. Further evidence of this can be seen in the histogram of the thel (below): the curve is not symmetrical as might be expected, but has significant contributions of higher micron fibers. This seemingly higher micron count of the thel was also observed in the Hamra samples.

Also seen in the sample of Hamra was a similar average micron diameter of the outer tog layer (45μm). This is the easiest tog layer to separate, and likely the only one removed when a thel/tog fiber distinction is make as even the intermediate tog requires close examination to identify it. However, the “tog” is reported in several sources (Abbott, 2001; Robson and Ekarius, 2011) to have a diameter of 27-31μm (50-56s), in the range of the inner and intermediate tog layers. The present results correspond well with those of several other adult sheep I analyzed in a previous Newsletter (Flowers, 2019); it is possible that the other published reports examined lamb fleede, as the fiber diameter numbers more closely correspond to the lamb fleece examined.

Now to answer the question: how do the number of fibers in each layer relate to the histograms of the individual coats? As it turned out, the graphs are complex. Therefore, because the equation of the curves is unknown, a physical gravimetric integration method (a.k.a., cut-and-weigh) was used. The histograms of the complete Dryngja sample and of individual layers, were standardized so that the x- axes (fiber diameter in microns) corresponded when the graphs were stacked, and the y-axis reduced to reflect the calculated percentage of fibers in each layer. Note that the final histogram, which is the second part of Figure 5, shows the actual contribution of the outer tog to the total fleece sample. Similarly, the thel, inner and intermediate tog layers are histograms reduced to show the actual contribution of these layers to the whole.

Histograms of complete Dryngja and of individual layers, standardized and reduced to reflect the magnitude of the calculated percentage of fibers in each layer.

Why would anyone care?

Besides the satisfaction of knowing what the actual numerical contribution of the tog layers is to the overall content of a fleece or a “lopi” yarn, what are some practical implications?

First of all, it is evident that the hand separation of the coats that most fiber artists might perform is only a rough separation by diameter of the fibers. This is unlike the mill process of “dehairing,” where the tog fibers are removed by weight so more of the shorter, thicker fibers would be separated out. These heavy tog fibers, however, are not retrievable for use (JC Christiansen, personal communication). For fiber artists who wish to use the long tog fibers, hand separation would be the appropriate method; if thel that lacks the shorter, thicker fibers is required, mill separation might be a better option.

Wool fibers that have a diameter <26 mm are suitable (fine enough) for clothing worn next to the skin, while fibers 26-30 mm may be used for clothing such as outerwear and socks. Larger diameter fibers are useful for household and industrial applications (e.g., rugs). Since the vast majority of fibers of the Icelandic fleece are found in the thel and inner tog layers, and the majority of these are 13-30 mm, a majority of the Icelandic fleece consists of lightweight fibers usable for the clothing industry. Despite the relatively large mass contribution of the intermediate and outer tog layers, relatively few fibers in the Icelandic fleece are available for use in products requiring coarser wool.

Finally, while there are slight differences in coat fiber numbers and mass between the two unrelated sheep, the results are remarkably uniform. This suggests that these results are transferrable to any fleece of the Icelandic Breed of Sheep.

Acknowledgment:
The technical assistance of Eric Hartmann, (Wells College, 2018, Mathematics) is gratefully acknowledged. Literature Cited:
Abbott, Elizabeth. 2001. The Icelandic Fleece: A Fibre for All Reasons. Self-Published. 96p.
Flowers, Margaret 2019. The Icelandic Fleece. ISBONA Newsletter 24(1):11-16.
Robson, Deborah and Carol Ekarius. 2011. The Fleece and Fiber Sourcebook. Storey. 438p

Originally published in the Newsletter of the Icelandic Sheep Breeders of North America - Summer 2019: Volume 24, Issue 3, Pages 30-33.