Bark River Black Compound (up close)

[HeavyHanded]

Hello all, this one was at Andy's request - a closer look at the Bark River black compound. On a Washboard applied to paper he described it as making scratch pattern close (visually) to a DMT fine at 25 micron. Am not sure what it looks like on paper over a flat surface, or on a leather strop (probably considerably less defined), but it appears to be a range from 10u to 30u with most falling in the 15-22 range. There are fines that are much smaller, but do not appear to compose a large percentage of the total by volume.

I've noted before that the effect from various compounds seems to be very heavily influenced by the binder as well as the rated grit of the material. I don't have much more than a fat pinch of the compound to do any testing, but typically the Washboard tends to get a lot of penetration from a given abrasive when used with paper at moderate amounts of pressure. Used with less pressure, multiple sheets of paper, on leather etc would probably appear a quarter or less than the actual, in line with how most stropping surfaces effect the scratch pattern at a given grit.

The abrasive appears very much to be white AlumOx as it is somewhat translucent. My own opinion is this is about where a compound leaves off and one would be better served with a fixed abrasive if using anything more coarse.

 

[Ernie1980]

Thanks for sharing this! I found that the edge from the black compound seemed pretty rough too so I stopped using it. The green leaves a nice finish. I also had trouble getting the black compound to stay on a strop in a nice layer, it wanted to clump up and then crumble off.

 

[AFAustin]

HH, thanks for looking at the BRKT black. That is a surprise---it seemed coarser than the 4 microns shown on the Grand Unified Grit Chart in the sticky, but your results are eye opening.

Andrew

 

[awestib]

Thanks for doing that Martin! I am glad I was not too off with my visual inspection!

 

[HeavyHanded]

HH, thanks for looking at the BRKT black. That is a surprise---it seemed coarser than the 4 microns shown on the Grand Unified Grit Chart in the sticky, but your results are eye opening.

Andrew

It definitely comes back to seeing is believing. I never know what I'm going to see when I do something like this. Most would be surprised at how uniform the particle distribution is even on the cheaper compounds, and how large some of the individual grit can be when it comes to the 'black' compounds. IMHO the better ones are defined more by the percentage of abrasive and how well the binder is formulated for a given application.

Personally in my "research" I've found that, on a conformable strop, grit values much smaller than 20-25u have a real tough time doing any amount of restorative work, and larger ones are just awkward to manipulate with any efficiency compared to a fixed abrasive. The 25u or so is perfect for this application, especially when you consider Bark River is formulating their compound primarily for working on full convex edges. That increase in surface area will tame it even a bit further but still leave enough bite to true the edge.



@ Ernie 1980, a drop or two of mineral oil can tame the grit as well as prevent it from clumping, gives it a bit more mobility and it doesn't bite as hard/deep as it probably does with the stock binder. Just go easy with the oil if you try this, maybe start with some compound on a sheet of paper wrapped around a combination stone.

 

[HeavyHanded]

Thanks for doing that Martin! I am glad I was not too off with my visual inspection!

Seeing is believing, you have to trust what your eyes are telling you (I don't need to tell you that!) even if you don't know for sure the whys and whatfors. Is possible to decrease the effective abrasive presentation, is very difficult to increase it, and impossible to make it present larger than it really is. If you see a 20 odd micron scratch pattern, there has to be a reason.

 

[Chris "Anagarika"]

Martin,

Thank you! I also use oil rubbed on the 'rocky' compound to make pastelike substance, then transfer these to paper on WB. Works well for edge restoration without going back to stone, for simple steel, followed with white & green (the real strop) :thumbup:

 

[ksskss]

Very interesting and useful information! Thanks! How were the particles selected for measurement and how was the measurement decided? By that I mean was it the widest dimension of the particle, average, smallest of just random? The smallest particles seemed to be ignored so it seems it actually is a much wider distribution mostly towards the smaller particle size. The pictures supplement the measurement data nicely.

---
Ken

 

[HeavyHanded]

Very interesting and useful information! Thanks! How were the particles selected for measurement and how was the measurement decided? By that I mean was it the widest dimension of the particle, average, smallest of just random? The smallest particles seemed to be ignored so it seems it actually is a much wider distribution mostly towards the smaller particle size. The pictures supplement the measurement data nicely.

---
Ken

It was all rigorously scientific of course! I applied some oil to a slide and with clean fingertip, put some compound on the slide and gently tapped it out to a uniform film. The sample was taken from a block by scrapping off with a piece of hardwood so no steel or glass fragments would contaminate the sample and any wood contaminants would be easily ID'd.

I panned across the sample and just found a region that was nicely separated from the binder (black clumps) and appeared to have a representative mix. I try to average the dimensions out somewhat, I have to choose the points to measure. Could apply a circle, square etc, but in the end a point to point is as accurate as anything else. Some were more than 30u measured at the widest, but I generally shoot for a diagonal - not the shortest distance but not the longest across either.

Some of the smallest particles might well be air bubbles trapped in the oil or tiny bits of binder partially broken down, but definitely if one were to mark up every spec you'd have quite a range down to single digit micron. I didn't see a ton of sub micron that could be ID'd as such, so tried to average it out. Not terribly scientific, but as I panned across the sample it did appear to have a pretty uniform distribution. Far and away the bulk by volume seemed to fall into a range of 10u being at the small end and 30u at the large, with most in that 15 - 22 range.

I'm fond of phrases like "seems", "appears" etc when doing stuff like this as I'd have to do a handful of times to be definitive. From what I saw it looked pretty consistent.

Martin