Curing of Glued Sinew over Time
Volker Tank from Germany hopes Members would answer the following question:
"For the process of making horn bows allowing the sinewed bow to cure
over longer time periods prior to tillering is often mentioned as
important for the bows' quality (at least half a year, better one year,
. . . ).
"Could you please post the question on ATARN: What actually
happens along the time axis during curing, for example after a day, a
week, a month, six month, a year. What will become better and what are
the physical/chemical processes causing that?"
"For the process of making horn bows allowing the sinewed bow to cure
over longer time periods prior to tillering is often mentioned as
important for the bows' quality (at least half a year, better one year,
. . . ).
"Could you please post the question on ATARN: What actually
happens along the time axis during curing, for example after a day, a
week, a month, six month, a year. What will become better and what are
the physical/chemical processes causing that?"
That is an interesting question. let me expand on it.
Does the longer time result in a more even reduction in moisture content, like wood seasoning?
Are there chemical changes like polymerization?
Are there physical changes like shrinkage which improve the performance of the bow?
Does the longer time result in a more even reduction in moisture content, like wood seasoning?
Are there chemical changes like polymerization?
Are there physical changes like shrinkage which improve the performance of the bow?
I am working on that right now.
Many can tell how to make sinew bows but nobody seams to know why and reasons.
First day, the sinew don't break and the glue hold it in place. But it's still soft so it bend when bow is drawn and takes no load so the wood can break.
One week, the sinew start hold against the bend.
Second week, it starts to add weight.
Third week it starts to shrink and pulls the in reflex if wood allow.
Many can tell how to make sinew bows but nobody seams to know why and reasons.
First day, the sinew don't break and the glue hold it in place. But it's still soft so it bend when bow is drawn and takes no load so the wood can break.
One week, the sinew start hold against the bend.
Second week, it starts to add weight.
Third week it starts to shrink and pulls the in reflex if wood allow.
I?ve yet posted that drying is the wrong explanation for what is happening.
It was Jim Hamm who has posted that a sinew-backing is dry after 2 weeks or so. That?s right. No more moisture will leave the backing, the moisture depends on the environment.
But much more important is the polymerisation, the main components of horn, sinew and glue are proteins (keratin). These are polymeres and what polymeres are doing is polymerisation: at first they make molecular chains, than these chains make crosslinks.
Polymerisation needs time and warmth.
It is definitely wrong to tiller a sinew-backed bow after 2 weeks.
The ancient bowyers are talking of about 8 months.
At one of my bow-classes last October I met a medical researcher focused on the polymerisation of bones and horn and he approved my presumption. He is just doing some research on the polymerisation of horn, sinew, hide- and fishglue for me.
I hope he could give us some more insight.
Michael
It was Jim Hamm who has posted that a sinew-backing is dry after 2 weeks or so. That?s right. No more moisture will leave the backing, the moisture depends on the environment.
But much more important is the polymerisation, the main components of horn, sinew and glue are proteins (keratin). These are polymeres and what polymeres are doing is polymerisation: at first they make molecular chains, than these chains make crosslinks.
Polymerisation needs time and warmth.
It is definitely wrong to tiller a sinew-backed bow after 2 weeks.
The ancient bowyers are talking of about 8 months.
At one of my bow-classes last October I met a medical researcher focused on the polymerisation of bones and horn and he approved my presumption. He is just doing some research on the polymerisation of horn, sinew, hide- and fishglue for me.
I hope he could give us some more insight.
Michael
A part of the answer is quite simple: The drying process is governed by diffusion of moisture through the layers. The rate of diffusion grows with a square of thickness. If one layer dries in one week, then two layers dry in four weeks, three layers in 9 weeks, 4 in 16 weeks etc. This would be a bit of an exaggeration though, since in our case the previous layer is already dry. But still, moisture does not only go to air, but also down into the first layer. So, given the thicknesses we deal with, and to be sure, the drying of something like 1/4 inch total (in some places on a bow) should be at least 4 months. This again depends on the ambient humidity and temperature. If we take 2 weeks drying for one layer, not one week, the drying time will be greatly exteded.
The other part is more complicated. I have done quite a bit of work on a similar subject in my day job as a (former) chemist. Once I am finished with a few experiments, I will write about it. "Polymerization" is here hydrogen bonding, but there are other processes too.
Adam
The other part is more complicated. I have done quite a bit of work on a similar subject in my day job as a (former) chemist. Once I am finished with a few experiments, I will write about it. "Polymerization" is here hydrogen bonding, but there are other processes too.
Adam
Polymerization typically requires enzymes which don't work in the absence of moisture. I don't think there is going to be substantial covalent bonding of collagen going on, maybe hydrogen bonding but I don't think we are going to see that much of a difference in the crosslinking of sinew after it is thoroughly dry. So I don't think it is polymerization per se that is what is going on with sinew. Besides, polymers are already polymerized to a great degree.
I subscribe to Adam's theory that it can take a long time to dry when a material is thick. Also consider that the wood/bamboo core will absorb some moisture and would release that very slowly since its covered with a thick layer of sinew and possibly horn on the other side. That to me, might be the slowest step of all, drying out the very core of the bow. Doesn't mean you can't do some bending though, since the core is under the least amount of stress since it should be centered around the neutral plane if the backing and belly are balanced.
I also think the recommendation of months of drying, might have something to do with the fact that bowyers of old didn't make one bow at a time, they made many. So each step would take them a week or more to perform on their multiple bows. It might take a whole year to complete thirty or forty bows, that is just how long it takes to do things on a large scale. And it is certainly a more effective use of time, to do each step on thirty bows at once rather than make each one from start to finish, one at a time. I thought of this when watching Duvernay's Korean hornbow video.
Also consider that there are seasons when the weather is advantageous to certain steps. For instance, a bow will dry more quickly in a dry season and/or one with warmer average temps. Keep in mind, these guys didn't have AC or dehumidifiers. So I think this also comes into play in the recommendations. We now have the advantage of artificially adjusting our surroundings to make them optimal for drying a bow more quickly than could be done in a simple uninsulated dwelling or even in a shed.
In short, I don't think it is always necessary to wait a year for sinew to cure. It is more dependent on your design and your environment. You aren't getting a substantial change in the length of polymer chains during this time. Nothing happens like that in a dry environment. There can be no movement of the ends of existing polymers, to get them in close enough proximity to allow them to link up and form a longer chain. Maybe there are hydrogen bonds formed, but these are not that strong compared to the strength of the covalent bonds of the polymers as they exist from the start.
Just my opinion.
I subscribe to Adam's theory that it can take a long time to dry when a material is thick. Also consider that the wood/bamboo core will absorb some moisture and would release that very slowly since its covered with a thick layer of sinew and possibly horn on the other side. That to me, might be the slowest step of all, drying out the very core of the bow. Doesn't mean you can't do some bending though, since the core is under the least amount of stress since it should be centered around the neutral plane if the backing and belly are balanced.
I also think the recommendation of months of drying, might have something to do with the fact that bowyers of old didn't make one bow at a time, they made many. So each step would take them a week or more to perform on their multiple bows. It might take a whole year to complete thirty or forty bows, that is just how long it takes to do things on a large scale. And it is certainly a more effective use of time, to do each step on thirty bows at once rather than make each one from start to finish, one at a time. I thought of this when watching Duvernay's Korean hornbow video.
Also consider that there are seasons when the weather is advantageous to certain steps. For instance, a bow will dry more quickly in a dry season and/or one with warmer average temps. Keep in mind, these guys didn't have AC or dehumidifiers. So I think this also comes into play in the recommendations. We now have the advantage of artificially adjusting our surroundings to make them optimal for drying a bow more quickly than could be done in a simple uninsulated dwelling or even in a shed.
In short, I don't think it is always necessary to wait a year for sinew to cure. It is more dependent on your design and your environment. You aren't getting a substantial change in the length of polymer chains during this time. Nothing happens like that in a dry environment. There can be no movement of the ends of existing polymers, to get them in close enough proximity to allow them to link up and form a longer chain. Maybe there are hydrogen bonds formed, but these are not that strong compared to the strength of the covalent bonds of the polymers as they exist from the start.
Just my opinion.
Horn proteins are called keratin and sinew and glue preteins are called colagen I think. :?
Horn proteins are keratin and sinew and glue proteins are collagen, this is right. But there are some other proteins inside these materials.
What a luck that the ancient bowyers didn?t have had dehumidifiers, otherwise I don?t think that their bows would have performed so well.
The most important process is the cross-linking of the molecular chains, and this happens definitely after the chains were built.
So it is obvious to find out how many time these processes need?
What is the best environment for these processes?
Does it makes sense to force them?
I think the ancient bowyers knew the optimal way to "dry" a sinew-backing.
Maybe we need another understanding of time. The so-called hightech-western-civilisations have a very simple understanding of time.
Many ancient cultures knew that time is a quality, nowadays this sense of time has been almost lost or has been advanced by people like Einstein or Picasso......
Time is much more than to count hours and hours till the sinew-backing is "dry".
Michael
What a luck that the ancient bowyers didn?t have had dehumidifiers, otherwise I don?t think that their bows would have performed so well.
The most important process is the cross-linking of the molecular chains, and this happens definitely after the chains were built.
So it is obvious to find out how many time these processes need?
What is the best environment for these processes?
Does it makes sense to force them?
I think the ancient bowyers knew the optimal way to "dry" a sinew-backing.
Maybe we need another understanding of time. The so-called hightech-western-civilisations have a very simple understanding of time.
Many ancient cultures knew that time is a quality, nowadays this sense of time has been almost lost or has been advanced by people like Einstein or Picasso......
Time is much more than to count hours and hours till the sinew-backing is "dry".
Michael
deleted duplicate post
As proof that there is NOT significant covalent crosslinking of chains in a sinew back, consider what happens to a backing when you attempt to recycle the sinew after a failure. After rehydration it comes back apart into the same individual strands that you started with. If there were some crosslinking action that happened in the gel stage or the solid matrix, then the sinew backing would remain as a single strip of material or at least in larger strands.
It is possible that sufficient dehydration weould bring enough of the external surfaces of sinew in close enough proximity to form hydrogen bonds and thereby strengthen the overall strip. However, this is simply a function of dryness and I contend that there is no evidence that it is superior to let a material dry naturally versus altering the environment to allow drying to proceed more rapidly.
You don't want to raise the temp enough to melt the glue before it has dehydrated properly. I've done this in my attempt to speed sinew along, and I think that is a mistake. If you see glue oozing out of the sinew during high temp drying, you are losing some of the bonding properties that it would otherwise offer when it was dry. So there is certainly a limit to how much you might be able to accelerate the drying process.
I would suspect that there are also some of the same pitfalls with speed-drying, as you find with the kiln drying of wood. Surface checking, case-hardening that leads to weakening of the interior material and/or slower overall drying due to creating a hard "shell", and unusual warpage are some potential problems of rushing a sinew backing to dryness.
It is possible that sufficient dehydration weould bring enough of the external surfaces of sinew in close enough proximity to form hydrogen bonds and thereby strengthen the overall strip. However, this is simply a function of dryness and I contend that there is no evidence that it is superior to let a material dry naturally versus altering the environment to allow drying to proceed more rapidly.
You don't want to raise the temp enough to melt the glue before it has dehydrated properly. I've done this in my attempt to speed sinew along, and I think that is a mistake. If you see glue oozing out of the sinew during high temp drying, you are losing some of the bonding properties that it would otherwise offer when it was dry. So there is certainly a limit to how much you might be able to accelerate the drying process.
I would suspect that there are also some of the same pitfalls with speed-drying, as you find with the kiln drying of wood. Surface checking, case-hardening that leads to weakening of the interior material and/or slower overall drying due to creating a hard "shell", and unusual warpage are some potential problems of rushing a sinew backing to dryness.
The major proteins of connective tissue in the (human) body are collagen and elastin. Tendon has collagen type I. Keratin is for skin and horns.
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Kollagen itself is already a polymer made of procollagen, the polymerization takes place with the help of enzymes in the space between the cells of the fibrous tissue. There are multiple proteins that cross-link the collagen strands. But tissue with only collagen (muscle tendons) is -not- elastic. It may only be streched minimally but not because the molecules are elastic but because the structures lie somewhat like waves (see pic). Elastin is needed for true elasticity.
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Tissues rich in elastin are the neck ligament (ligamentum nuchae), some of the intervertebral ligaments (ligamenta flava), the aortic wall, ear+nose cartilages. Loss of elastin in the skin makes it look "old" ie wrinkeled.
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One should think it would be better to use the neck ligament for making bows, but only theoretically (who tried it?)
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Once again, tendon alone is not elastic, not even when still living. Its plastic. Only muscle and elastin are elastic.
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So I think the secret is in the glue - and its interaction with water and collagen.
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Kollagen itself is already a polymer made of procollagen, the polymerization takes place with the help of enzymes in the space between the cells of the fibrous tissue. There are multiple proteins that cross-link the collagen strands. But tissue with only collagen (muscle tendons) is -not- elastic. It may only be streched minimally but not because the molecules are elastic but because the structures lie somewhat like waves (see pic). Elastin is needed for true elasticity.
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Tissues rich in elastin are the neck ligament (ligamentum nuchae), some of the intervertebral ligaments (ligamenta flava), the aortic wall, ear+nose cartilages. Loss of elastin in the skin makes it look "old" ie wrinkeled.
.
One should think it would be better to use the neck ligament for making bows, but only theoretically (who tried it?)
.
Once again, tendon alone is not elastic, not even when still living. Its plastic. Only muscle and elastin are elastic.
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So I think the secret is in the glue - and its interaction with water and collagen.
Uli, the essential parts of fish- and hideglue are collagen.
Thanks for all your contributions and insights, but I really want to wait for the results of the research an expert is doing for me.
I?m a craftsman with a deep interest in the scientific and philosophical background of ancient bowery.
Michael
Thanks for all your contributions and insights, but I really want to wait for the results of the research an expert is doing for me.
I?m a craftsman with a deep interest in the scientific and philosophical background of ancient bowery.
Michael