In my one-year yourney into hornbows I have worked only with ostrich, cow and pig sinew, all ahil tendons..
-pigs tendon sinew feels pretty soft and pliable in hands and doesnt feel any more greasy than ostrich/cow .... I have managed to cut out maybe 10-13cm in length max ... but pigs legs are not cheap at all - because some people eat it as specialty - and butcher sells them well !
I tested it only - glued on bamboo board
-ostrich feels a bit coarse compared to cow and pig, even more when shreded to the tiny parts (looks like thicker), I have used it for first layer in my present project...when combed with korean method - it absorbed the glue and get even thicker ?
more than cow sinew ! For second layer I used cow tendons... (I run out of ostrich)
I bought ostrich sinew from pet shop but there is problem with these pet food processors - they obviusly dry the tendons in heat - and you get a lot of damaged tendons (shrinked or turned into brown crystals - glue !) - I used the damaged ones for glue ...
There are pictures of dried cow tendons (actualy young beef) which I extracted.
They throw away whole leg (under the knee) - I managed to cut out the tendons leading to the finger-cave (in hoof), pretty tedious labour !