Hemp strings and heavy bows

[WillS]

I've been doing a lot of research into natural fibre strings recently, and thought I'd share my (eventual) success with you guys.

I knew I wanted to use hemp, based on the small fragment found on the Mary Rose and the few historical documents mentioning hemp as bowstring material.  It's also one of the strongest natural fibres on the planet, as well as one of the longest so it makes perfect sense to use as a bowstring. 

The problem however is sourcing good quality hemp.  I've been importing hemp fibre from all over the world with little success, and finally decided to cut, ret and process my own.  I have a contact here in the UK that has an industrial hemp farm so I went over and selected my own hemp stalks to use.  They're about 3m long stem to tip.

The stalks were retted in the garden (not recommended - the smell is unbelievably awful as the cannabis plant starts to rot!) peeled the fibres from the stalks and ended up with a huge bunch of beautiful soft hemp fibre.

The fibres are twisted together in the traditional Flemish manner - a reverse-twisted three-ply laid-in top loop, no twist throughout the body of the string except to keep the fibres tight together (so no reverse-twist, essentially) and then a reverse-twisted tail in which a bowyer's knot is tied.

My requirements for these strings were fairly straightforward - they had to work with sidenocks, they had to support bows over 150lb and they had to be no larger than about 2.5mm

Eventually, after lots of failure and experimentation I hit upon the perfect glue mix for the strings - fish hide glue (not isinglass) and vegetable glycerine in a fairly high glycerine to glue ration to keep the string glue flexible. 

These pics are of the latest string, which is 2mm thick and holding nicely on a new 155lb bow that I made quickly.  The bow is nothing particularly special, it's not made to any dimensions but just roughed out by eye and feel from a piece of pale English yew.  I needed something brand new so that the brace tension was as high as possible, with a finished draw weight of 150lb+ but didn't want to spend too long on it.  I think it was just over an afternoon's work.  It's not even got a finish on it yet!  It'll probably just be a "string tester" instead of being shot, so that it's always really punchy and gives the string a full workout.

[peacefullymadewarbows]

That second cow horn nock is a looker. That's really impressive. I'm not familiar with historical natural materials strings. Was it common for them to glue them? I guess I ask because other than rubbing on some beeswax we have the modern luxury of just being able to reverse twist our strings together and have them hold fast. Can the hemp not do that? Thanks for the post and that's a beautiful bow nonetheless.

[WillS]

Cheers!  Well we just don't really know to be honest.  There's one document from the 17thC that suggests strings should be "gummed and not glued" presumably to avoid the brittle, hard nature of glue.  That doesn't help much however, as the word glue could have meant something different back then, and the distinction between gum and glue could simply be the addition of a plasticiser to make it more flexible. 

From the experiments that I've been conducting, it seems that if you're very lucky and get perfect fibres with no thicker or thinner areas, you can get away with just waxing the string.  However, that's extremely rare (especially today, because nobody is harvesting hemp for bowstrings so I was forced to use lesser quality stuff) and using glue homogenises the fibres into one solid item, so the areas that would otherwise be weak become as strong as the rest (within reason).

There are other documents that describe medieval bowstrings as "hard and round" which is certainly the end result of a glued string. 

If using short-fibred material such as linen however, the only way to make a string is to reverse twist everything, otherwise it all comes apart under stress.  You can either buy or make yarn or twine or cord which is all reverse-twisted - for instance Barbours 18/3 is a very common reverse-twisted yarn used for bowstrings - and pretend it's like FastFlight etc, running it end to end and just twisting up the loops, or you can reverse-twist the entire string which is what I tend to do with linen for heavy bows. 

The beauty of hemp is that it's one of the only natural plant fibres that grows beyond the length of a bow - 2m is common, and 3m is perfectly achievable.  This, coupled with its immense natural strength means you can simply peel the fibres away from the inner stalk or hurd and essentially tie it to both ends of a bow.  I've done that just as a proof of concept and had no problem with bows up to 140lb.  It's ugly and thick and very primitive but it shows the strength of hemp.  By separating the large peeled strips down into thinner sections and making nice tidy loops you end up with a very elegant solution using that natural length and strength.

(By the way, welcome to PA and I did read your Instagram message, and will get back to you with some dimensions! I've just been crazy busy at the moment and haven't had time!)

[peacefullymadewarbows]

Interesting. Yeah an etymologist would be handy to have on hand to figure out that document with more assurance haha. Where I live we have stinging nettle which was used by the Native Americans for bow strings. It can get to about 1.5-2m without branching. Not soon, but once I have more patience and more experience cutting proper sidenocks (and some european cow horn for that matter haha) I'd like to try to go start to finish making a bow string for one of my 100lbers to start. So your string posts have been motivating for that.

And no worries at all! Just been very eager to go about a proper MR replica now that I'm getting the hang of making a good general heavy longbow. Your work is very appreciated and motivating. Just let me know. 

[JNystrom]

Looking good Will. Now, shoot it!
So if the string was glued with this mixture, it wouldn't really weather proof even with wax on it. Well i don't know, wax is really good at protecting from moisture.
How does the hemp stand abrasion? Looks like you served the loops.

[WillS]

You could wax over it once dry.  As long as it was kept waxed it should be fine, but hemp is actually very good in damp conditions.  It gets stronger when it's wet, and is very rot resistant.

Hemp is poor against abrasion, hence the serving.  It's not necessary to protect against the actual force, but the string won't last long without it.

[FilipT]

How many strands and what is the thickness of individual strand? Btw, have you tested strands for breaking, if you did, at which poundage do they break?

[WillS]

There are no individual strands so it's impossible to say.  Theoretically it could be combed out into hair-thickness fibres but it's not necessary so I have no clue what the breaking strength is.

One plant, loosely twisted will hold over 200lb and another identical thickness plant will break at 40lb.

[willie]

great you are doing this. some bast fibers have the best strength peak at certian times of the growing season. were your plants harvested with an eye towards max strength?
can you share what you have learned about any retting do s or donts?
thanks

[DC]

And while you're at it maybe a short essay on the care and feeding of hemp strings . Do you keep it in a plastic bag or leave it on the bow, what do you look for as far as wear is concerned, that kind of stuff. Now that cannabis is legal in Canada I might try to grow some hemp.

[Hawkdancer]

Very interesting thread!  Hemp has just been designated a a "crop" rather than a drug in Colorado, so I expect to see more and better crops, hopefully some emphasizing fiber.  I remember that hemp was a huge crop before and during WWII, for both rope and fabric, but then faded due to the "pot is evil" hysteria, then revived a bit as a controlled substance.  I'm sure we will relearn a lot of things about hemp fiber strings!  Good luck!
Hawkdancer

[WillS]

Glad it's of interest!  It's certainly the missing link between now and then, as making historical bows and shooting historical arrows with modern Kevlar strings doesn't quite get the answers does it!

The hemp was not grown for fibre strength at all, but for oil and textiles so it's far from perfect.  I'm looking into getting it grown purely for long, strong fibre next season but it's just not a viable marketplace at the moment.  No farm is going to be interested in losing an area of potential income by growing for bowstrings!  As for growing them yourself, it's crucially important that the right strain is chosen.  The hemp for smoking is no use, and some industrial strains are just too weak or don't grow high enough.  The trouble now is that there are endless hybrids for different end results and we're probably nowhere near the stuff originally grown for bowstrings.  An industrial hemp growing license here in the UK is around £600 at the moment, so that's not in my future anytime soon!

The retting wasn't perfect as it was my first time and all the available information is dealing with fibre for textiles, so soft with a good colour is the usual end goal.  I think in future retting it for a shorter time period would be best.  It's a very difficult balancing act between retting long enough to release the fibre without it stripping towards the end, and not too much so that maximum strength is achieved.

The strings are kept on the bows, simply because the glues stiffen them up.  They could be kept coiled up somewhere and unwound for use, but I've not made enough to do this yet.  I've also not been shooting them long enough to know the ins and outs of looking for wear.  At the moment when they decide to snap, they just go but I'm sure as my familiarity with them grows I'll start noticing the warning signs. 

[Strelets]

Will, this is very interesting and important research.  Have you thought of submitting it to the Society of Archer Antiquaries ? I am sure that they would want to publish it in their journal. 

[willie]

An industrial hemp growing license here in the UK is around £600 at the moment, so that's not in my future anytime soon!

understandable. Perhaps you might be willing to share what your research has turned up about the desirable (for bowstrings) strains? No license required here anymore.

[WillS]

Will, this is very interesting and important research.  Have you thought of submitting it to the Society of Archer Antiquaries ? I am sure that they would want to publish it in their journal.

I've had articles published by the SAA before and wasn't ever particularly impressed by the results but I'll be presenting the hemp strings to the Guild next year I think, and as many members are in both organisations perhaps I'll discuss it then.

An industrial hemp growing license here in the UK is around £600 at the moment, so that's not in my future anytime soon!

understandable. Perhaps you might be willing to share what your research has turned up about the desirable (for bowstrings) strains? No license required here anymore.

I wish I knew what it was!  Next year I'll make sure to get those details and I'm still researching which strains are best for which purpose but as of now I've got no idea.