Testing marked ropes to failure


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Trad climber
Morgan Hill, CA (Mo' Hill)
Topic Author's Original Post - Dec 11, 2010 - 02:48pm PT
I like a center mark on a rope but I don't like what bi-color ropes cost so I thought I'd check the influence of some different markers on rope strength. My results should be considered preliminary and I think there are some problems with them. This is my first effort at testing rope and I had to debug test fixtures and had some uncontrolled, non-quantified variables. I thought I would post what I got anyway even though the results were highly variable and inconsistent. I did not measure the resilience, brittleness or the energy absorbed by the rope. Being an old rope, there was certainly variation in condition from piece to piece.

Being cheap, I used an old (15 or 20 years) rope that has been doing garage duty for some years. It looked to be in pretty good shape and wasn't even fuzzy. I've climbed on worse looking ropes and possibly older ropes. I don't recall using it as a toprope or that it took many falls but that it was retired due to age. I had used it mostly in the alpine, backcountry environment. It is a full dynamic rope of uncertain diameter and I'm not sure but believe it to be a dry rope. I don't know what manufacturer.

I cut 16 pieces from the rope and tested half of them tied in a loop with a double fisherman's knot and the other half as a single strand tied at each end in a clove hitch.

For each type of test I did two pieces unmarked, two marked with Sharpie, two marked with Rub-a-Dub (a fabric marker by the same people that make Sharpies) and two marked with a Marvey fabric marker. I totally covered the surface with the marker, much more so than you would actually do to a rope.

I believe sharpie is solvent based but don't know for sure.

Rub-a-Dub is marked as non-toxic and I think is water based but I don't know.

The Marvey/Uchida markers came in a 6 pack of primary colors with "bold tip" and were labeled as non-toxic but doesn't say water based or non-acidic.

For the clove hitch tests I marked the part of the rope that would be in the knot at each end. All clove hitch tests all broke at one of the knots.

For the loops, I marked the section that would pass over the 1/2 inch pins at each end. All of the loops broke at one of the pins, not at the knot.

My hypothesis was that solvent based markers (sharpie)and water based acidic markers would reduce the strength. The Rub-a-Dub is supposed to be non-acidic but I don't know for sure. Marvey makes markers labeled as non-acidic but they didn't have any at the local fabric store so the ones I used may or may not have been acidic. Blue Water suggests using Rub-a-Dub to mark ropes:

My results are all over the place but it looks like markers do reduce the strength. I won't suggest you mark ropes but if you do have a mark on a rope, I would advise you not to tie loaded knots at the mark or have the mark at an anchor. Anything you do to a rope can only reduce its strength, the question is how much.

If I ever redo this type of testing, I would make sure to try a water based, non acidic marker. I would also use new rope. I would measure the energy absorbed by the rope or do impact testing.

Loop test video

Clove hitch video


Dec 11, 2010 - 09:31pm PT

I loosely weave dental floss into the sheathes of my ropes at the center point, which is just as visible as ink and not much chance of rope damage. The floss breaks and frays, which makes it even more visible. Plus if you have stuff in your teeth mid-route, you have floss.

Trad climber
Morgan Hill, CA (Mo' Hill)
Topic Author's Reply - Dec 11, 2010 - 10:47pm PT
QITNL - Yep, the stuff stretches more than I expected. To do dynamic tests you would need to have enough drop to allow for stretch. I have a 1200 lb steel block and a Peck & Hale "quick release hook" of 4500 lb capacity. The hook is pretty neat and allows you to drop a load by yanking a cord:
Just pick up the block with a forklift and hang the rope sample from a load cell. I just need an overhead anchor that is high enough, strong enough and stiff enough.

I haven't written off rub-a-dub yet since my results are pretty scattered. I don't think it will make your rope stronger though.

MURCY - I have a couple ropes with yarn woven through the sheath at midpoint. I use an blunt embroidery needle to weave it in. For yarn I use a strand worked out of the sheath of an old climbing rope which is pretty tough and comes in bright colors.

Trad climber
The state of confusion
Dec 11, 2010 - 10:54pm PT

I'm curious how your test might work with pre-marked ropes,
like Beal. (I'm not quite ready to retire either of mine),
but it'd be interesting to know how they came out
compared to your tests.

And even though you used sheltered ropes, I wonder about
using younger ropes too.


Dec 11, 2010 - 11:39pm PT
This Crimmons guy is pretty sharp. I can't remember the number of times I have needed floss - when the leader is midpitch. On occasion I have even had to drop belay because of this.

These tests being all on ruined old ropes, I am going to go put floss into my ruined old ropes. That's the advantage ruined old climbers have over everyone else.
jack herer

Veneta, Oregon
Dec 11, 2010 - 11:57pm PT
I've heard that Marks-A-Lot brand pens are good for marking ropes.

Does any one know if this true?


Trad climber
100% Canadian
Dec 12, 2010 - 01:03am PT
It's best to mark ropes, like you mark your territory, by pissing on them

Trad climber
northern CA
Dec 14, 2010 - 12:01am PT
Thanks for posting! It's always interesting to see actual numbers.

If you do more tests, I'd be curious to see results for a water-based acrylic paint.

Some background:

In the olden days when rec.climbing was the only climbing forum, sometimes it seemed like one of the most popular/successful trolling topics was ANYTHING related to rope marking.

But occasionally things appeared that seemed to make sense, one of which was a post that I copied, saved and, amazingly, could still find after all these years:

The recommendation: do not mark your rope with any kind of felt pen. Water-soluble acrylic paints are apparently safe. No information is available how long they stay on.

(I can paste in the entire post if anyone is interested.)

Anyway, the water-soluble argument seemed plausible to me and several years ago I got some acrylic paint from a local arts supply and marked my 70 m rope. (According to the time stamp on this picture, it was actually 5 years ago. I think I intended to post about this on ST at the time but, obviously, I'm a good procrastinator. Especially since the original rec.climbing post was from the mid-90's!)

However, I never considered the possibility that there might be acids in a water based paint. Anyone know anything about acrylics?

I guess the real the question is:

Was I gonna die?
Clint Cummins

Trad climber
SF Bay area, CA
Dec 14, 2010 - 02:43am PT
If we assume an additive linear model, even with the small sample,
you are close to getting statistical significance for Marvey at the usual 95% level:


Trad climber
Mountain View, CA
Dec 14, 2010 - 02:50am PT

Bob Culp at the old Boulder Mountaineer recommended the Sharpie T.E.C. (Trace Element Certified) marker for ropes. You might want to test one of those next time around.

Karl Baba

Trad climber
Yosemite, Ca
Dec 14, 2010 - 03:59am PT
How long did you leave the marks on the rope before testing.

I have to imagine that weakening substances often take time to weaken. Battery acid after an hour on a rope is different than battery acid on a rope for years



Trad climber
Morgan Hill, CA (Mo' Hill)
Topic Author's Reply - Dec 14, 2010 - 11:35am PT
I forgot to add a couple details. The ropes were all marked on 11-17-2010 and tested on 12-9-2010. The results are in pounds.

I considered water based paint since I think a non-acidic water based product will be the best but hard to say if a paint is acid free. I think it would be best to stay away from a generic category since not all paints are equal.

Best bet might be an archival, acid free India ink. Faber-Castell makes an archival, acid free, India ink marker called "PITT big brush artist pens," probably worth the $2 for something that is not generic and probably has reliable chemistry. They also claim to be waterproof.

I would be willing to test more pieces, anybody want to donate some new rope? Perhaps even cut, tie and mark the pieces. I spent way more time scribbling on ropes that I did testing them. Talk to Clint but I would think three to five samples with and without marks might be a good idea. My gut feel is that the loop test will have less variability and that I should test with a standard carabiner. The loop test is pretty hard on the rope since as the knots tighten, the rope drags over the edge. Since the rope works over the edge, you also have to mark a fairly big section.

Clint- I need a little math lecture, I didn't do any sort of statistical analysis other than to observe that the scatter was big and the sample small. What do you conclude from your analysis?
Brian in SLC

Social climber
Salt Lake City, UT
Dec 14, 2010 - 12:11pm PT
Best bet might be an archival, acid free India ink. Faber-Castell makes an archival, acid free, India ink marker called "PITT big brush artist pens," probably worth the $2 for something that is not generic and probably has reliable chemistry. They also claim to be waterproof.

Can recall researching into this awhile back, when it came up on wreck climbing and thereabouts.

Seem to remember that one reason folks couldn't rely on Sharpies, and various other pens, was that they used different solvents as carriers, and, some were worse than others for nylon. Some benign, while some degraded nylon. Same pen, different solvents. Can't recall which were bad, which were ok.

I think there's too much spread in your data to make any solid conclusions, but, its interesting for sure. No surprise that the clove hitches broke at the knots. Probably not much of a surprise that the loops broke at the 1/2" pin. I would think the loop test would have more fidelity for what you're trying to see, as, a clove hitch might have more variation in results just due to using a clove hitch. Big spread in both your control samples in both tests.

What I think would make an interesting test, is, to find a couple of fair sized pins, say, 3 to 4 inch in diameter, to wrap the rope ends around, apply your sharpie (etc) to the middle of the strand, and, pull to failure. In other words, try to eliminate the variability of the hitch and 1/2 radius bend as the weak spots, and, pull to failure the rope with and without marking.

Also, looks like you're just failing the sheath. I wonder if you could bump up the test speed, and, get the whole rope to bust?

Neat stuff. Thanks!

-Brian in SLC

A long way from where I started
Dec 14, 2010 - 12:31pm PT
This whole debate is so last century.

Just get a bic lighter, fuse the two ends of your rope together. Then every point on the rope is the middle and you can stop worrying about it.


Big Wall climber
Hugo, MN
Dec 14, 2010 - 01:01pm PT
Just a thought.

Since the question is: Does marking a rope weaken it?

Why do you have to use 10-11mm (normal) climbing ropes? Why not use 5-6mm (or smaller) cord? Seems like you could run more samples at lower cost.
Greg Barnes

Dec 14, 2010 - 01:15pm PT
How about the adhesive from climbing tape? A fair number of people wrap climbing tape around rope mid-points (repeatedly since it falls off sooner or later)...

Trad climber
Mountain View, CA
Dec 14, 2010 - 01:27pm PT
One other thing worth looking at is the penetration of the ink into the core of the rope. Is the marker just affecting the strength of the sheath or does the ink also penetrate to the core?

I think this is important because, as I understand the design of kernmantle ropes, the sheath is just supposed to protect the core while the core is supposed to be what provides the strength and elasticity to hold falls.


Trad climber
Yacolt, WA
Dec 14, 2010 - 01:52pm PT
The data is interesting to me. First is the concept of weakening the rope by marking it. We stopped that practice a few years ago given an article published about that weakening the rope. However, I didn't recall seeing any data.

Another question for me was the effect of aging and use on rope. Rescue teams get into huge dabtes about their soft goods reitrment policies. We are engaged in one now about when we should retire our ropes. There isn't a lot of published data.

Curious - what kind of rope did you test and do you know the original strength?


Trad climber
Morgan Hill, CA (Mo' Hill)
Topic Author's Reply - Dec 14, 2010 - 03:31pm PT
Seamstress - It's just an old rope I had. I don't recall who made it, what diameter it is or if it was dry. I have pictures of me using it nearly 20 years ago.

From the white dork thread:

Dec 14, 2010 - 03:49pm PT
how many of the marked samples actually failed at the mark?

It seems to me that's the real question here.
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