Tuesday, January 30, 2007

Blade Surfaces - Viking Age

Posted by Gus to Hammered out bits at 1/29/2007
" I have a question about finishes for historical knives. I really like bright shiny finishes, but what would the historical record say about shiny finishes. Is there a way to speculate on this from the historical record? "

Is there a way to examine artifacts and determine their original polishing level?


Since I know Gus, I suspect what he is referring to here are blades from the Viking Age. (This a continuation from yesterdays post and recent article, which yes, did not cover that aspect.)

Almost without exception, any blades still in existence from the early Middle Ages or pre-Conquest will be heavily corroded. Any iron based object tends to oxidize with time back into what is basically rust. The level of corrosion is typically quite high for Viking Age objects. So much that even information on exact measurements of the starting object is hard to determine. (As an aside, this should be taken into account when looking at descriptions on things like weights especially. What will be listed is the CURRENT weight - which may be quite different than what the object was when 'new'.)

Since the original surfaces are gone, we have to look at other things to determine what finish may have existed on the blades when they were produced.

As any blacksmiths know who may be reading this, it is unlikely that the original forged edges were taken down to much less than about 1 mm (say 1/32"). Although a talented smith might be able to forge thinner than this, doing so while maintaining an even straight line is so difficult as to be basically a waste of effort.
Any pitting on the surface of the blade would certainly be removed by grinding. Again depending on the skill of the smith, the number and size of these forging marks will vary. I know with my own work (some skill and higher temperature coal fires) I expect to remove at least something between .5 to 1 mm off each surface of a blade. Note that this combines with the degree of forging so that by the time I get the surface smooth, I've pretty much reduced the thickness at the edge to a sharp line. For purely functional reasons, we can expect any historic bladesmith to have also removed any forge marks. Any imperfection in the surface creates a potential weak spot where stress would become concentrated. A forge pit on a blade becomes a spot that may cause failure of the blade in use, either a crack or even the blade shattering across. So for this reason, you should expect a historic blade to be flat and clean on the surface.
A secondary check on this would be looking at the references to especially swords in the Sagas. Often there are descriptions of how blades 'flash in the sun' or otherwise brightly reflect light. A clear indication of the use of clean metal surfaces.

Next what we need to consider is the tools available for the work of that grinding. Just as pits can become potential break points, any deep grooves or scratches in the surface can do the same thing. (Note I'm not talking about fullers here, which run parallel to the cutting edge. Fullers reduce the metal volume while at the same time they create a more complex structural shape. These are added, particularly to sword blades to reduce the overall weight of the blade but at the same time maintaining the resistance to bending.)
Files are found in blacksmith's tool collections from the Viking Age. These are hand cut using a chisel, and are thus rough and irregular. Although they might prove of some value for the initial roughing out of the blade contour and surface, they really are too course a tool for actual polishing. Bare in mind that these historic files are made of metal with only a slight amount of carbon in it. In most cases they would be no harder than the metal in the blades themselves. Most polishing in this period is fact done with stones. Primarily what we find are hand stones, and relatively small ones at that. There is not way to think of the process of first flattening and then polishing a blade surface using hand stones except extremely tedious. I have seen a couple of narrow cylindrical grind stones from the period, mainly as fragments. These are all small and so likely equipped with simple hand cranks.
Any way you look at, the use of natural stones, moved by hand over the blade surface is going to put an upper limit on how fine a polished surface would be possible. We do know that good quality whetstones were a common trade item in the Viking Age. The ideal stone would have an even texture, and stones of differing grits ranging from course sandstone to fine shales are found. Through a long and careful process of working down through ever finer grits it is in fact possible to produce an extremely polished surface.
I doubt personally however that fine polished surfaces would have been the norm during the Viking Age. So much of the material culture of the Norse shows a stress on FUNCTION over mere form. Once you have reduced the rough forged surface of the blade to flat and without pits or scratches, there is little functional reason to polish any further.

I have a circa 1880 foot peddle grind stone tucked away in the shop. This was actually retrofitted at some point with an electric motor and pulley to drive it, though all the original peddle mechanism is still in place. This stone is roughly 2 1/2 feet in diameter and a bit over 2" wide (say about 75 cm x 5 cm wide) It hangs in a water trough in use. When I created one of the knives for the Norse Encampment program, I quite intentionally finished one side using this stone. On the opposite side I used modern tools - in this case the 6 x 24" belt sander with a 100 grit belt. It proved easier to maintain a perfectly flat surface with the belt sander and the cutting rate with the modern tool was a bit quicker. With a bit of care used on the large wheel however, the two surfaces are almost impossible to tell apart.

Taken altogether, my gut reaction is to guess that knives in the Viking Age would be in fact ground to be flat and clean - as is consistent with producing a high quality tool. The surfaces would be polished bright, but unlikely much beyond what would be seen with a contemporary 80 - 120 grit belt.

Now what happens to PATTERN WELDED blades is a whole other pail of fish. (And yes - I'm working up that article too...)


As a personal opinion, I stay away from highly polished surfaces on blades. The current trend to mirror polished surfaces is a reflection of 'knives as ornament' as opposed to 'knives as tools'. Although considerable care and skill (or the right expensive tools) is required to produce an even mirror finish, it is not desirable for a working tool. A mirrored blade is almost totally impossible to sharpen - a single swipe of an oilstone that is not absolutely correct scratches that surface and mars it. I consider all the knives I produce to be working tools and so normally only polish to 180 grit to produce a 'satin' finish.

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