Rosin Isn't Adhering to New Bow Hair?

September 29, 2025, 11:11 AM · Press harder. I stick my fingers between the stick and the hair on a fresh bow so I can really work it in. There's no such thing as a bad batch of hair, really---it's all hand-picked at several points from horse to bow.

September 29, 2025, 11:21 AM · Is the rosin that ultra-hard imitation glass? Either score it with a knife or bin it and buy better. I've never had difficulty starting a new block of Guillaume. Or is there some way the hair could be greasy? If so, the alcohol should have dealt with that.

September 29, 2025, 11:47 AM · How old is the rosin? It has a shelf life of maybe a couple of years.

September 29, 2025, 12:32 PM · Thanks Andrew. I scored the rosin and that was an improvement. Then I added some swipes of viola rosin and the bow seems back to normal! Nate, have you found old rosin has reduced grippiness? My Liebenzeller and Andrea rosins are about 5-6 years old

September 29, 2025, 1:56 PM · I use Bernardel rosin and I have experienced no deterioration in the rosin over time. However, I also like to combine old fragments and broken pieces of rosin by melting them together in a silicone mold. I notice that the rosin emerging from this process is a little harder and requires more pressure to apply. I speculate that there is a small amount of water (or some kind of small-molecule substance) in the rosin that plasticizes it, and this is partially lost to evaporation when the rosin is melted in my oven. I've tried adding a few percent of water during the process without noticing any benefit. It's not an insane idea -- phenol-formaldehyde resins which are used to make caps for bottles and jars are known to be plasticized by water.

My own feeling is that the most important reason why a combination of rosin and bow will seem to deteriorate is that the bow hair becomes dirty. It can be cleaned with alcohol using isopropanol "prep pads" or using grain alcohol. After that, the bow hair itself has a finite lifetime, but the rosin, in comparison, is essentially immortal. In a few million years, it will have converted to amber.

Edited: September 29, 2025, 4:27 PM · Cotton Mather wrote:
"There's no such thing as a bad batch of hair, really---it's all hand-picked at several points from horse to bow."
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I will vociferously disagree that there is no such thing as a bad batch of hair. Yes, most hair may be hand-sorted, but where do you suppose the lesser hair from this sorting process goes?

Since horsehair is no longer much used to stuff car seats or reinforce plaster, will postulate that it goes to the rehairers who are themselves either oblivious to the differences between great and crap hair, or who believe that nobody will be the wiser if they cheap out.