Best fibers for making any kind of cordage come from long backstrap sinews, but long leg tendons (e.g. from a moose or a deer) work well, too. After the tendons have been preprocessed (refer to the Internet) and dried, the sinew fibres need to be extracted. This process is described abudantly in existing literature, for example by Stevenson (1995; 1997: 13-17), Karpowicz (2008: 58-61), Hamm (2000: 214-221) and Baker (2000c: 231-233). In addition, there are several Internet resources that are even more highly recommended:
- 1/5 Sinew bowstring: a video on Youtube
- 2/5 Sinew bowstring: a video on Youtube
- Sinew cordage tips: a video on Youtube
- Preparing Genuine Sinew for Sewing
- Sinewing a bow
- How to process backstrap sinew
Process step-by-step Edit
The process for breaking tendons is sinew fibres is very straightforward. You take a leg or backstrap tendon and beat it with a stone, a hammer or a wooden mallet until the fibers start separating. At least on deer leg tendons the color of the tendon changes from brown to white when this is happening. Make sure that whatever you use does not have any sharp corners: you do not want to cut the sinew fibres. Also, for the same reason, use only just enough force to separate the fibers.
Once the tendon has been well beaten, you can take the tendon and start ripping it into pieces. A good strategy is to rip the entire tendon into two parts, split those and then split until the desired fibre thickness is reached. In practice, it doesn't seem to matter much whether you start splitting from the ends or from the middle. If you have trouble getting splits to start, you can use a thick needle or a sharpened piece of hardened, round steel (~3mm thick) to get you started.
How thin is thin enough? Edit
Extracting the sinew fibres is the slowest part of the sinew cordage making process. There are several contradicting requirements that determine the optimum fiber thickness:
- Short fibers need to be twisted more tightly than long fibers to make strong (single-ply) thread/cord
- Thick (single-ply) thread/cord twisted N times won't be as strong as thin one for it's weight, as the outer fibres need to spiral around the outside along a longer path than in thinner cord twisted N times.
- Splitting tendons into (too) thin pieces tends to produce short fibers
- Halving the thickness of the fibers doubles the amount of time spent ripping them apart
So, if we split tendons in very fine thread, we spend a lot of time and get fairly short fibers, which we need to twist tightly to make durable thread. If we split tendons into very thick fibers, we use far less time and end up with long fibers that don't need as much twisting to make durable thread. All in all, in the case of siew, it does not make sense to aim for very fine thread: the negative impact (time and shortening of the fibers) counteracts any benefits thus gained. Also, sinew as a material has a couple of properties that make making of good-quality cordage easier:
- It stretches a lot before breaking (5-10% or more), so the loss of strength caused by twisting sinew into thick single-ply is neglible
- Moisture dissolves the inter-fibre glue in sinew, binding the fibers together
- When sinew thread/cord is pulled, it stretches and it's diameter is reduced. This means the fibers squeeze tighter and tighter against each other when more load is applied.
With non-stretchy and non-gluey materials such as flax, following the traditional wisdom of thread/cordage making ("thinner is stronger for it's mass") is important. With sinew, this is not true to the same extent.
All in all, a probably good compromise is to split the tendons to ~0,5mm thickness. There are several reasons for this:
- The amount of work required is fairly small (comparably so)
- You don't have to pay too much attention to what you are doing
- The fiber bundles rarely split when left this thick
After this point splitting will become more difficult, as you need to use a sharp needle to get a split started. You would also have to pay attention to avoid breaking the fibers and to make split at the exact middle of the fiber bundle.