My thoughts on why some brushes may shed.

I wanted to take a few moments to share my thoughts on why some brushes may shed, either initially or after months to years of use. It is a common topic here on B&B and I am by no means suggesting I am right or that my thoughts are all inclusive, rather, I wanted to share some of my experiences along with some pictures which may help explain why some brushes shed.

As with almost anything else in life, the outcome of an event is often shaped by several variables, and I suspect the same is true with brushes which shed. Though some of those variables are user-dependent, i.e., user care, frequency of use, etc, some are not and that is what I hope to address in this post, at least in part.

Most knots have hairs/bristles which are set in an adhesive base, commonly referred to as a knot plug. I have used and held knots from several vendors and while the type of adhesive/epoxy used for this process may be different, there seems to be one universal truth to almost every knot I have held in my hand- there are bubbles in the adhesive base, or knot plug. While the bubbles are small, some near microscopic, they are always there and essentially represent a void in the plug. This is not a criticism of any vendor/supplier, simply an observation and an unavoidable truth.

Here is a knot from a well respected vendor I and many others use. Due to the color of the adhesive, it is hard to see the bubbles in the plug.


Here is the same plug under 30x magnification with my loupe. The bubbles are readily visible now and appear innumerable.


Here is the same knot, showing the same plug from the side demonstrating macroscopic bubbles along the upper edge of the plug.



I use a similar epoxy to set my knots in place and I hope to demonstrate how these bubbles come about and how they, coupled with regular use/care, may contribute to some shedding.

Here is a freshly poured 2 part epoxy commonly used to set knots into a handle. As you can see, when both parts are dispensed, there are no bubbles present.




However, even mixing the 2 parts VERY slowly, yet thoroughly, lots of air is introduced to the mix and due to the viscosity of the substrate, remain, even when fully cured as I hope to demonstrate in the following post.

Here is the same piece of epoxy, now fully cured and as you can see, the bubbles remain. The edges and surface faces are smooth save the fingerprint smudge at about 5:00-6:00



I decided I would take this fully cured epoxy sample and submerge it in a solution of cold water and vinegar in a 1:1 ratio for 5 minutes, as many of us use a water/vinegar soak to clean our brushes.



Here is the epoxy sample after the 5 minute soak. As you can see, the surface of the epoxy has been severely etched. Equally impressive was the change to the edge of the same where the epoxy had begun to break down. In fact, an entire film or skin was created over the sample which I was able to easily peel away.



Here is the same sample under 30X magnification after the water:vinegar soak.


I think this may add weight as to why many recommend, myself include, NEVER soaking the full knot of your brush, at least not while cleaning it; particularly if you are using the water:vinegar method described in the brush care wiki. As I mentioned earlier, we all have different habits with our brushes so this clearly is not applicable to everyone but I still wanted to share.


However, most of use do soak our brushes before use and this got me curious as to what happens to the adhesive with hot water exposure without the vinegar. I hope to address that in the next post.

I took another fully cured sample of epoxy and soaked it in hot tap water for 5 minutes. I used my tap water, on full hot for the experiment.

By nature, the epoxy I use is somewhat flexible, even after fully cured, and this is a property I appreciate as the knot will suffer several different forces during lather building and facial application while in use. I guess you are looking for the bend but don't break balance for the adhesive.

However, I was surprised to see how malleable the epoxy became after a 5 minute soak in hot tap water. I was able to bend the epoxy with MINIMAL pressure immediately after removing it from the hot water.



As the epoxy cooled, over a matter of 2-3 minutes, it rapidly lost this degree of flexibility and became increasingly rigid until.....



It did not take a great deal of pressure to cause the epoxy to fracture after it had cooled. Thus another reason to avoid soaking your entire knot, particularly in hot water.

So here are some of the conclusions I have drawn both from my experience and this little experiment-

1. Almost every knot will have bubbles in the glue plug if an adhesive is used. These bubbles represent voids in the plug and if the gauge of the hair is small enough, those housed in this void may eventually shed, particularly after exposed to some type of physical and or chemical stress. I suspect this may be why boars shed less as the gauge of the bristles is far greater than badger hair.

2. Hot tap water alone may certainly influence the flexibility of the glue plug and or/the adhesive used to set the knot in the handle, albeit temporarily. However, it does appear the epoxy becomes increasingly rigid as it cools and this rigidity, coupled with physical stress of using the knot may increase the risk of shedding or hair fracture, particularly if the hairs reside in the aforementioned bubbles of the glue plug. This may also help explain why some knots simply dislodge from the handle entirely. Given this observation, I feel, as many others, it is always best to soak only the majority of the knot in cool water only. I would recommend against soaking the entirety of the knot regardless of water temperature and would avoid using hot water for any reason.

3. When the epoxy is exposed to the vinegar in the vinegar/water cleansing method, it may be damaged as demonstrated above. PLEASE DO NOT MISUNDERSTAND THIS POINT- I am not saying this is a dangerous method of cleaning your brush. I use this method all the time with excellent results, but I NEVER soak the entire knot in the solution. I see no advantage in doing so and as demonstrated above, there may be negative consequences either to the adhesive used in the glue plug or the adhesive used in setting the knot in the handle.

4. Even in the absence of bubbles in the glue plug adhesives, fractures may occur as the adhesive cools and the hair loss from such could be catastrophic (overkill word given what I am discussing but you get the point).

Now, let me say, I realize there are several limitations to the conclusions I have drawn from the little experiment. I realize I am likely using a different epoxy than several vendors use. I also realize the thickness of the samples I used are far less than the average glue plug depth of 8mm on most knots. Again, I simply wanted to share some observations I have made and if I am able to help one person here, it is worth it.

If you took time to read the entire entry, thank you for your time.

I think you are onto something Joe.

Excellent post! Thank you.

very informative, thanks for your testing ... ill be sure to not submerge my entire knot in water now!

Very helpful information you provided, thanks for the work and the write up.

Thanks, Joe, for your tests and observations, which are certainly informative.

Joe; Superb posts. You are to shave brushes what Achim (Mr-Razor) and Chris (Xillion) are to Gillette! I always wondered about the mild acid of vinegar's effect on shave brush hairs also. That's why, like you, I now use Leonhardy brush cleaning soap from The Superior Shave which you kindly instructed me on how to use.

Nice observations! I also have an unproved theory that very dense knots with finer badge hair may be prone to shedding due to the increased "displacement" of the epoxy by the hair. Or perhaps its just coincidence that my denser brushes shed more.

Makes sense to me. Well done and thanks Joe!

Thanks for the insight, Joe. A great post that is difficult to fault.

This is good science to laymen who don't really understand what goes on behind the scenes. Thank you for some very good piece of work and information. This belongs here as a sticky and a permanent place in Shave Wiki !

Extremely useful post!

Thanks for taking your time to do this, it will change my cleaning routine for sure!

Excellent analysis Joe.

This type of post really speaks to the information sharing and the value that one gets in B&B.
Thank you!
I myself have been known to soak my brush in hot water prior to my shave. I will no longer be doing this.

Interesting post, Joe!

Very useful. Thanks!

I have no idea what brush makers use as their glues or epoxides, however after reading up the chemistry it seems that epoxide would be rather unstable in water over time. The stuff is vulnerable to both acid and base catalyzed nucleophilic substituions. Anyway, I also read some epoxides are more water resistant. That would probably be what you want, and it would also probably be less vulnerable to the same acid and base catalysis.

i know nothing about brush manufacturing though.

Where but on B&B would you find someone who would go to such depths to investigate an occurrence that most think of with little more thought than..... "well it happens sometimes"

Good work and a nice well presented argument to back up what I have always tried to tell folks, if it is too hot to stick your hands in for a few minutes it is too hot for your brush.

I've never used anything stronger than a mild dish soap (1-2 drops in the palm of my hand then palm lathering) to clean a brush, followed up with a good lathering with the MWF