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Bubbles in sinew backing?

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Marin:
Hey guys,
This is an issue I have always noticed when I sinew back though I think it comes down to aestetics, since I haven't had a bow fail because of this.
I often find as my sinew backings dry small bubbles appear to form in the backing. They don't appear too deep or seem big enough to cause adhesion problems. I once thought it was because my hide glue (I use store bought knox gelatin) was too thick. Thus, I always keep my hide glue on the thin side, more like thin syrup/slighty thicker than water as I have heard it is best made, so I don't think it's this problem. I make sure to soak the sinew, usally for an hour or more. I also dip it several times in my glue pot or even lay it in there for a couple seconds to make sure it's fully soaked in glue. If I have to quickly add a new strip, I may only soak it for a couple minutes in water until it feels soft, and often chew it several times to aid in quick softening. I'm curious if this is the problem, but the bubbles appear to be in multiple areas regardless of how long the sinew strip is soaked. Maybe it has something to do with glue temperature? I usually keep the glue around the temperature of hot bath water; hot enough to steam slightly but not too hot that it burns my hand or ruins the sinew.
I have attached pics of what I am seeing. The bubbles are hard to see but if anyone has had this problem before, this might look familar to them.
Am I right in assuming that this is more of an aethtic issue and not something that will lead to future problems? If it is, is there a way to fix it?

Phillip King:
I would Try Rolling them Out with a Burnisher Or Mini Rolling pin

Pat B:
Try lightly rubbing your finger over the spot. Where the sinew has adhered well to the wood the sound will be muted but where there is a bubble it will sound hollow.
 How did you prepare the back of the bow just before adding the sinew? Were your hands clean? It doesn't take much oil from a finger or a drop of sweat to prevent adhesion. Your glue consistency sounds about right and your sinew prep sounds good so IMO it is possibly there was contaminants(oils) on the bows back at sinewing time.
 If it is in fact oil on the bow it might be difficult to repair. You might try heating the areas where the bubbles are and wrapping it until completely cooled.

superdav95:
I can’t see the bubbles you speak of in the pics but so long as they are not air bubbles I would say they are more asthetic and shouldn’t be a performance issue.  How are you laying your sinew down?  Do you lay down smaller shorter sections of bundles or do you lay down longer more measured layers?   In the past When I’ve laid several smaller bundles of sinew I noticed irregularities in the surface of my backing that I believe were the some of the feathered ends of the bundles curling up or twisting underneath other bundles.   Hard to know for certain but a possibility.  It functioned fine but this may be the same thing you’ve seen in yours.  I now since have switched my sinew method to longer more measured layers.  FWIW

Marin:

--- Quote from: Pat B on June 12, 2023, 09:52:55 am ---Try lightly rubbing your finger over the spot. Where the sinew has adhered well to the wood the sound will be muted but where there is a bubble it will sound hollow.
 How did you prepare the back of the bow just before adding the sinew? Were your hands clean? It doesn't take much oil from a finger or a drop of sweat to prevent adhesion. Your glue consistency sounds about right and your sinew prep sounds good so IMO it is possibly there was contaminants(oils) on the bows back at sinewing time.
 If it is in fact oil on the bow it might be difficult to repair. You might try heating the areas where the bubbles are and wrapping it until completely cooled.

--- End quote ---

I washed my hands quite often before and during sinewing. To prepare the back I used soap and water and then brushed acetone on top and let that evaporate. I did that twice just to be sure. And this is also not the first layer but the second/third so it’s not adhesion to wood issues.
I did have to move the bow while it was drying but after the glue had gelled so I don’t know if touching it during drying caused any issues.

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