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Wednesday, 2 September 2015

Fire (2/2)

Fire (2/2) - The Experiments

While the archaeology provides evidence for the use of firesteels, and there is linguistic evidence for the continued use of friction-fire in the Migration Period and Viking Age, there is little archaeological information to aid reconstruction of the full fire-lighting process which likely required a range of specially prepared materials, allowing cool sparks to be nursed to roaring flames.

To fill these gaps in knowledge it is necessary to experiment with techniques and materials that would have been locally available at the time, taking inspiration from modern bushcraft techniques and, importantly, other cultures from similar ecoregions (with similar materials available) which have maintained traditional firelighting skills that may be similar to those used by our ancestors.    

Our investigation into the fire-making process is ongoing, and we do not claim to be experts with respect to such techniques. However, we have attempted a number of experiments with locally available materials, informed by available information on modern bushcraft fire-lighting, and the techniques employed by other traditional cultures. It is worthwhile discussing the feasibility of many of the materials traditionally used, in terms of their availability or value in a rural Migration-Age West- European context, and their effectiveness when prepared using the technology available at the time.



(The first chapter of this series, concerning cultural aspects relating to fire, and the archaeological, linguistic and cultural evidence for fire-lighting methods can be found here)

While essential for cooking and warmth, particularly in historical contexts like those that interest us, hearth-fire represents the culmination of an elaborate process necessary to overcome various challenges associated with the materials involved. Timber does not, itself, readily burn. Instead, temperatures sufficiently high to allow pyrolysis and volatilization of the solid material are required - often in excess of 300 degrees Celsius. To reach this point using a cool spark from a fire-steel, or "two sticks" is a tall order. It is for this reason practitioners emphasize that those trying for the first time should not feel discouraged by failed attempts, nor should the achievement of a successful attempt be downplayed.

Technique
As previously discussed, hearth-fires in the Migration and 'Viking' Ages were 'sparked' by use of flint and steel, or by friction methods. Ferrous strike-a-lights are not uncommon grave finds, occasionally symbolic but sometimes functional, providing good archaeological evidence for this part of the process, while evidence for the use of friction fire comes from a range of non-archaeological sources (see previous article).  However, these represent a relatively small part of the process necessary to create fire.

Flint and steel, with two tinders (charcloth, left, and prepared F. fomentarius block right)
Historic fire-making before the age of matches, lighters and accelerants was necessarily a multi-stage process, whereby a series of fuels were used, beginning with highly flammable fuels able to ignite with little activation energy, burn fast and hot, and graduating progressively onto denser, slower-burning fuels only combusting at high temperatures. While in the Migration Age and earlier peoples would have had little knowledge of the chemistry behind this process they certainly would have had an intimate knowledge of the practical process, passing down the technique from generation to generation, experimenting with variations, and refining it.
With both steel-fire and friction-fire a number of materials are required; primary tinder, secondary tinder, kindling and fuel. Tinder is normally understood as any material with a large surface area which will burn fast and hot enough to allow wood kindling to catch, and most often, with modern 'bushcraft' fire-lighting techniques, dry moss, grass or straw are sufficient. Here, we refer to these as "secondary tinders", as historic techniques require additional tinder defined by a different criterion; a low enough activation energy threshold for ignition to occur when in contact with a relatively cool spark or speck of fire-drill dust.

Secondary Tinder
Paradoxically, secondary tinders are worth considering first, being as they are by definition consumed quickly, and a good handful is necessary for each fire-lighting. Although suitable secondary tinders can be found just about anywhere, they must be bone-dry. This is easily achieved with good shelter and the warmth of a fire, so its worth giving thought to your tinder supply for the next night, before you let any fire die !
One favorite is moss. Although invariably sodden, moss dries fast and burns hot and quickly - perhaps too quickly, making it a good secondary tinder, though with the tendency to sometimes burn itself out, or fragment and blow away after insertion into a wood stack.  The key with moss, it seems, is to ensure the 'nest' being used to nurse the burn is well compacted; this will slow things down a little and hopefully allow enough time for heat to build, and  flames to appear.
Alternatively, dry long grass and straw both make for excellent secondary tinders. As with moss, a dense 'nest' around the primary tinder should be made, such that, once flames have been produced, the nest can be inserted into the timber stack and hopefully raise temperatures high enough that the kindling will burn, eventually spreading onto logs. These materials seem to burn a little slower than moss, which could be an advantage, but also, we think, burn a little less hot. However, a considerable advantage of straw is its tendency not to fragment and blow out of the stack quite as readily as moss, allowing more time to encourage the flames to catch onto kindling.
With each of these tinders a well compacted fist-sized 'nest' is desirable, but if a fire need be lit quickly using only the contents of a compact portable kit, dry birch-bark is a reliable, very flammable alternative which can be used, even in relatively small amounts, to nurture a piece of smoldering tinder into a flame.

Primary Tinder
For reasons of clarity we refer here to materials intended to ignite on contact with a spark (or friction-dust) as 'primary tinder'. Primary tinder should have low enough activation energy threshold to ignite when hit by a cool spark, and burn fast and hot enough to raise the temperature high enough for secondary tinder to ignite. While it is in theory possible to light foraged materials with sparks (especially with modern "Scandinavian" firesteels), in practice, reliable fire-lighting requires pyrolysed material; either specially prepared tinder, or using the naturally generated charcoals from a previous fire.
Pyrolysis is simply the thermal cracking of organic molecules, in low oxygen conditions, to produce more reactive "char" materials. In theory such materials require lower activation energy (heat) to trigger ignition, therefore being ideal primary tinders for catching and growing sparks.
With charcoal crucial to metallurgy and smithcraft during this period it is impossible to argue that the Anglo-Saxons and associated cultures were not regularly producing and making use of pyrolysed materials, and, though charcoal does not make a particularly good primary tinder, it is conceivable that the Anglo-Saxons may have harnessed the process to make specially prepared primary tinder for reliable fire-lighting.  This process could have been conducted concurrently with charcoal making in clamps, or in a domestic setting within a lidded pottery or stone vessel beside the fire.
Though a char can be made from any organic material, not all such chars make decent tinders. It is further important to consider the availability of materials in the context concerned.


  • Wood Charcoal

It is not particularly easy to get charcoal to ignite using only flint and steel. However, charcoal generated in-situ and left among the ashes of a previous fire can be re-ignited by casting sparks on them. This approach takes a few tries but is effective, and may have been an approach routinely used, at home, by our resourceful ancestors. Partially charred coals generated in-situ from a previous night's fire in a house or hall may often have still been warm, and would certainly be reliably dry, making this 'free' tinder arguably the first resort in domestic contexts.   Wood shavings, specially pyrolysed, do accept sparks more easily than lumpwood charcoal, though not readily, subsequently burning quite fast and not especially hot. This demonstrates that, with primary tinders, it is not simply a case of pyrolyzing any dry plant material.


  • Charcloth

The go-to tinder among enthusiasts of the flint-and-steel method is "char-cloth". This black and brittle material is easily made by heating small pieces of cotton cloth, in anaerobic conditions, to high temperatures until flammable gasses stop being emitted. Given charcoal was a crucial part of the ironworking process in the Migration-Age and earlier times it is impossible to argue that such 'prepared pyrolysis products' were not available, and they are almost essential for success with the flint and steel method.   However, there is no evidence to suggest cotton was available in Britain during the Migration-Age, and if it had been, it must surely have been a prized luxury commodity.
Though all guides I have seen on modern bushcraft advocate 100% cotton for char-cloth making, it seems entirely equal results can be achieved with linen - a cloth locally available in Migration-Age western Europe, though still thought to have been something of a luxury.  We have found no difference between cotton and linen -based char-cloth, in terms of ease of use. It could therefore be argued that charred linen cloth could have been used as primary tinder in the Migration-Age, itself made from small scraps of linen cloth - byproducts of the making of garments.        The problem with this idea is that rare, extant examples of clothing from around the time of the Migration-Age in western Europe show an extreme conservatism with respect to fabric, with clothing patterns carefully designed to minimize waste of valuable (and laboriously produced) cloth. Further, with linen being a luxury material, and with most clothing fashioned from wool, the idea that most communities would have routinely had access to an abundance of linen scraps is problematic.
In terms of utility, char-cloth is an adequate tinder but not the best. Sparks do take, often after a few tries, but the glowing cloth then burns up very quickly; time is therefore of the essence for getting the embryonic fire to catch onto secondary tinder. Sparks tend to "take" best when they hit exposed frayed edges, as fibres locked into a tightly spun and woven structure tend to less readily combust. "Roughing" the brittle charcloth by rubbing it can negate this to some extent and allow sparks to catch more readily.
With a more open structure with greater surface area for contact with oxygen, nests of pyrolysed linen thread catch sparks readily, otherwise having similar properties to linen charcloth. Such tinder could be produced from scrap threads from weaving, but again, the availability of such tinder would depend on access to a linen industry. Where possible, it is likely scrap threads would have typically been recycled rather than consigned to burning.


  • Charred Flax Fibre

While scraps of woven linen cloth could have been pyrolysed to produce a reliable primary tinder, there is no reason to suppose that the same plant fibres, not yet spun and woven, would not have made at least as good a tinder when pyrolysed. Here, we are indebted to the leaders of  Worcestershire Young Archaeologists, who had grown flax in their allotment and, at a 2014 joint event at Bishops Wood Centre were busily processing the flax (now retted) into fibres for spinning - breaking up and separating out the straw from the fibers, and rejecting any fibers found to be too weak or short. The Young Archaeologists team were kind enough to supply us with a quantity of rejected flax fibre.

Retted flax fibres (centre) amongst other flax byproducts (f;lax straw etc)
Once pyrolysed, small 'nests' of fibres were found to work brilliantly as primary tinder, catching sparks more readily than char-cloth, and burning hotter, igniting secondary tinder much more readily. The material, if anything, could be described as "too effective", with flames produced seconds after sparks had 'taken'. This otherwise fairly worthless byproduct of linen production would have been available in abundance anywhere where flax was grown and processed, and its conversion to tinder seems more feasible in a Migration-Age context than scraps of hard-won linen cloth. The processing of nettle-fibres in this period for use in clothing, too, would likely have yielded byproducts suitable for tinder-making; something which may be worth further research
.
Charred flax fibres ignited using a spark from flint and steel


  • Fomes fomentarius - "Tinder-", "False Tinder-" or "Horse Hoof Fungus"

Fomes fomentarius (FF) is a rot fungus commonly found on Beech and Birch trees in temperate regions. A perennial fungus, Fomes fomentarius grows sizable, hard-shelled polyporous fruiting bodies (brackets) containing rich brown flesh suitable for various uses, most notably tinder. This fungus would likely have been available in abundance in temperate decidious woodlands of much of Migration-Age Europe, and likely well known. Today this fungus is recognized by survivalists as perhaps the best tinder material available in our ecoregion, though notably inferior to the so-called "True Tinder Fungus" Inonotus obliquus found in Boreal regions. FF fruiting bodies (along with flint and iron-pyrite) comprised part of the fire-starting kit found with the early Bronze-Age ice-mummy "Ötzi", discovered in the Austrian Alps in 1992, suggesting the use of this fungus as tinder was known to ancient Europeans. It is not inconceivable that this knowledge persisted into the Iron-Age and Migration Era.

Fomes fomentarius  fruiting bodies in situ

F. fomentarius under microscope. Porous surface, top, and below, transverse section showing tubes in porous layer, and soft suede-like tissue (yellow) beneath shell, ideal for making tinder. 
With respect to the UK, various modern bushcraft sources claim this fungus is not readily found outside of Scotland and perhaps the far north of England, and throughout most of England occurs only on Beech. Our numerous trips hunting for these valuable fruiting bodies have shown this not to be the case, with the fungus being, in our experience, relatively easy to track down in mature Birch woodlands at least as far south as the Midlands, normally co-occurring with the more abundant and often more obvious Piptoporus betulinus (Birch polypore or razorstrop, discussed later). Searching fallen trunks and boughs near trees featuring visible razorstrop fruiting bodies may therefore represent a good strategy for tracking down FF. The fruiting bodies of FF can be distinguished by their usually dull grey shell, incredible hardness, and a fragrance not dissimilar to apples.
When pyrolysed, the flesh (and particularly the soft suede-like 'Amadou' layer directly beneath the shell) makes excellent primary tinder, catching sparks readily, becoming an incredibly hot and reliable smouldering coal. The intensity and duration of the heat emitted allows secondary tinder to be lit easily, with little need to rush the process (unlike with char-cloth).   We have had little success igniting un-charred FF tissue.    It is interesting to note that the more abundant Birch polypore, both charred and uncharred, does not accept sparks at all, highlighting the unique properties of FF.

Smouldering block of pyrolysed Fomes fomentarius (tinder fungus) lit a spark from flint and steel. 
A side note on Birch Polypore (not to be confused with FF);
Piptoporus betulinus - Birch Bracket Fungus or "Birch Polypore"
A pathogenic infection on common Birch trees, and almost ubiquitous in mature temperate stands of silver birch, the large fruiting bodies of this fungus have long been known to have a wide range of useful properties, from blade-sharpening (hence it's nickname "Razorstrop fungus") to antiseptic and anti-inflamatory wound dressings, and are quite distinctive, reaching large size, with a pure white porous underside, and an overall heavy but slightly spongy texture.
Piptoporous betulinus fruiting bodies in situ.
Piptoporus betulinus under microscope, showing porous underside (below) and cross-section (above) with porous layer and rubbery tissue (top). 
As far as fire-lighting goes, this fungus makes a poor tinder in comparison to it's distant cousin Fomes fomentarius (tinder fungus, or horse-hoof fungus) but is easier to find. The underside of the fruiting body is composed of a spongy and moist porous surface adapted to facilitate sporulation, while the upper half (cap tissue) of the fruiting body is composed of a dense, tough rubbery material which is flexible when moist and papery when dry. While the porous tissue has a musty "mushroomy" smell, the rubbery tissue when dried and separated from the porous surface has a mild, honey-like aroma.
Birch polypore is notable in that the non-porous rubbery tissue burns well but incredibly slowly, maintaining a cool smoulder without a flame, which gradually spreads through the material. As a result, a full fruiting body lit at the stalk can remain lit for many hours, with the outside remaining relatively cool to the touch. When doing this, the gradual burn is further supported by the porous layer, with each pore rationing the supply of oxygen to the interior. These fruiting bodies can therefore be used to safely carry 'flame' on long journeys, ready to light a fire the next time camp is made without the need to resort again to flint and tinder, or friction-fire. It has even been suggested, by some survivalists, that these fruiting bodies when lit can be used as rudimentary 'hot-water bottles'.
Our experiments have shown that a roughly one-inch square strip of the rubbery tissue (approx 3mm thick), when dried, takes 30-50 minutes to burn, maintaining an extremely stable and cool 'smoulder' sufficient to light fires from. This represents an extremely safe way to transport flame, especially when compared to alternatives such as a lit splint.
Birch polypore would have been available in abundance during Anglo-Saxon times, particularly in areas historically dominated by a forest-heathland mosaic. We have clear evidence of it being used by European Bronze-Age man (having been found in the posession of 'Ötzi the Iceman', either for medicinal or fire-lighting purposes) and it is conceivable that this fungus would have continued to be valued through and beyond the Iron-Age. The fruiting bodies are distinctive, easy to collect, and often reach enormous size (with large ones capable of yielding over 100 splints as described above).
Our attempts to use processed birch polypore cap-tissue as a primary tinder have not been successful. Though readily lit from a flame, the material does not readily accept a firesteel spark and allow it to propagate.
We have had some success lighting partially burned birch polypore strips, which seems to take a spark better than either the unburned dried tissue, or fully pyrolysed / charred tissue. This indicates charred polypore may be a reasonable primary tinder, although not an ideal one. The principle value of this fungus, as far as fire-making is concerned, seems to be in its ability to carry and maintain a flame that has already been made.  

  • Daldinia concentrica - "Alfred Cake Fungus"

A rotting fungus found on ash (Fraxinus spp.) Daldinia concentrica (DC) is relatively easy to find in locations where its host is prevalent (usually locations with relatively basic soils). The black ball-like fruiting body of this fungus (reminiscent of a particularly badly burned cake) contains concentrically arranged layered tissues which, when dried, can reportedly catch sparks from flint and steel, and can be used as primary tinder.
Our experiments with Alfred Cake have been more limited, as it is rare in our 'neck of the woods'. So far we have had no luck lighting chunks of dried DC flesh with flint and steel, although this fungus works very well pyrolysed, roughly equivalent to FF. 



______________________________________________________________________

The importance of fire in historic times, and the availability of reliable methods to make it cannot be overstated. With respect to the Migration and 'Viking' ages archaeology cannot provide all the answers with respect to the fire-making process. However, reliable tinders could be produced using methods known to have been used in the period, using materials readily available either in a domestic, agricultural or 'village' context, or else outside settlements, particularly in wooded environments. Whether any of these approaches were used may never be clear.    If these various tinders were used in our historic period of interest it is likely that the tinder of choice would probably be determined by convenience as much, if not more than efficacy.    In a domestic context, straw and the charred remains of previous fires would probably be used most often, while, on journeys through 'wilder' territory foraged materials may have been favored.    

Fire-lighting with historic methods is certainly very rewarding; it certainly feels like a fire thus made burns brighter and warmer for all the effort lavished on making it!


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