Collection: Field Notes - Regenerative Materials | 

Series: Natural Ropes | 

The Tar lubricant-preservative distinction, what each traditional dressing actually does, and where the evidence gets complicated

A distinction that took me too long to find

The most useful thing in the Atkins and Purser trials is not a result. It is a framing that appears early in the paper and that I missed on first reading, then found myself returning to: the lubricant function and the preservative function are separate. They serve different purposes. The best treatments do both simultaneously, and the ones that do only one — or that do both but in different proportions — perform correspondingly differently in the water.

The US Government rope specifications the authors cite required lubricant content of 8–12% by weight of rope as sold. Not preservative content. Lubricant content, specified independently. Because a rope that is well preserved against bacterial decay but runs dry inside under working loads is still cutting itself from the inside with every cycle of tension. The mechanisms post covers this in detail. The practical implication here is that evaluating a dressing by asking only "does it prevent rot?" is asking the wrong question, or at least not all of the right questions.

What follows is an attempt to work through the main dressings honestly — what each does, where the evidence supports the claim, and where I am less certain than the sources sometimes sound.

Stockholm tar

Already covered at length in the previous post. The summary for this context: it is hydrophobic, biocidal through its phenolic fraction, and lubricating. It addresses all three failure mechanisms simultaneously, which is a significant part of why it became the default for working rigging rather than any of the alternatives. Its limits are a performance ceiling that copper-tar combinations exceed, and a handling quality on frequently worked rope that some people find unacceptable. Both of those are real constraints, not mythologies.

Linseed oil

Linseed oil is where the received wisdom gets most confidently wrong, and where working through the chemistry carefully changes what you actually do.

Raw linseed should not be used as a standalone rope dressing. This is not hedging — it is the honest position based on how the oil behaves. Raw linseed oxidises very slowly, taking weeks or months to polymerise fully within the fibre bundle. In the interim it maintains a moist, oxygen-limited internal environment that is not unfavourable to the anaerobic variants of the bacteria responsible for rope decay. It also goes rancid rather than curing in cold or damp conditions. I have opened rope treated with raw linseed after a wet autumn and found it smelling of something between old cooking fat and mildew, the fibres tacky and slightly softened rather than consolidated. The oil had not cured. It had colonised.

There is also the spontaneous combustion risk, which is real enough to warrant naming directly every time linseed is discussed. Rags, waste, and any absorbent material contaminated with linseed oil during application must be spread flat outdoors to cure, or submerged in water. Never bundled in a confined space. The oxidation reaction that cures linseed generates heat, and a pile of oily rags in a locker can reach ignition temperature without any external flame.

Boiled linseed oil cures faster than raw — the name is misleading, it is raw linseed with metallic drier compounds added to accelerate polymerisation — but introduces manganese or cobalt driers that are a genuine environmental concern in a marine context. The driers are soluble heavy metal salts, and on rope in contact with seawater they will leach. For rope that stays above the waterline, boiled linseed is a reasonable dressing. For rope in immersion, heat-bodied linseed — polymerised by heat rather than chemical driers — is the version that makes sense. It cures faster than raw, contains no metallic additives, and produces a tougher, more water-resistant film on the fibre surface.

What linseed does well — in any of its forms — is lubrication. Applied warm to rope, it penetrates the outer fibre layers and reduces internal friction. A hemp sheet dressed with warm heat-bodied linseed has a particular quality in the hand — supple, slightly glossy, the fibres moving easily against one another — that a tarred rope does not. For running rigging handled daily, this matters. A rope you reach for willingly is a rope you maintain.

Where linseed falls short is biocidal protection. Oxidised linseed produces some phenolic degradation products that inhibit certain organisms, but it is not a meaningful bactericide on its own. The Atkins and Purser nets paper tested linseed oil combinations directly and found that linseed did not preserve tensile strength any better than copper oleate alone — it appeared to reduce the rate of leaching, but did not compensate for reduced biocidal activity. For rope in sustained seawater immersion, linseed as a standalone dressing is insufficient. As a lubricating maintenance treatment between tar applications, or as a carrier for a biocidal compound, it earns its place.

Tallow and beeswax

Tallow — rendered beef or mutton fat — is the oldest rope lubricant in European maritime practice. Bushell mentions it as a standard consumable aboard ship, used for the lead line, block sheaves, and rope running over chafing points. It appears in the rigging guides without ceremony, the way salt appears in a recipe.

As a rope dressing tallow is purely a lubricant and a temporary one. It has no biocidal action and limited moisture-barrier properties — animal fats are hydrophilic enough that water displaces them from fibre surfaces over time. On a boat tallow-dressed rope also attracts certain marine organisms, which creates its own problems. Its value is as a short-term lubricant for rope running over sheaves and fittings, not as a preservation treatment for rope in sustained seawater exposure.

Beeswax is different in character. Solid at room temperature, it melts in the palm at body heat — that slight resistance as you press it into the rope end, then the give, the wax releasing into the fibre — and it is genuinely hydrophobic rather than merely fat-like. Applied warm to rope it penetrates the outer fibre layers and leaves a firm, clean-handling surface. It has very mild antibacterial properties from its propolis content. It is not a meaningful biocide, but as a lubricant and moisture retardant for rope used predominantly dry — lanyards, end treatments, decorative work — it is pleasant to use and entirely appropriate. Do not rely on it for rope in sustained immersion.

Cutch

Cutch — catechu, from the bark of Acacia catechu — is the treatment with the longest history and the most underwhelming trial results, and the gap between those two things is worth examining rather than papering over.

The cutch and tannic acid post in the canvas series covers the chemistry in detail. For rope, the summary is that the Atkins and Purser trials found cutch produced 17% retained strength after ten and a half months against 13% for the untreated control. A marginal improvement, statistically barely distinguishable from doing nothing. Atkins' 1928 nets paper found it more effective on hemp than cotton, but still far behind copper soap treatments across all conditions.

The reason, as best I can reconstruct it from the chemistry, is that tannin-protein binding — the mechanism that makes cutch effective in leather tanning and in treating protein fibres like wool — has limited application to cellulosic rope fibres. Tannin does bind to cellulose to some degree, and it deposits a slightly hydrophobic layer on the fibre surface. But the binding is weaker and the layer thinner than what tar or copper treatments provide, and it does not persist under sustained leaching in seawater the way a properly applied tar does.

What cutch does do is change the way subsequent treatments behave. Atkins' nets work shows that cutch as a pre-treatment before copper soap improved results on hemp. The tannin layer appears to improve adhesion or retention of the copper soap, though the mechanism is not fully established in the literature and I have not tested it directly. For cotton rope specifically, where the near-complete absence of lignin makes the fibre particularly vulnerable, cutch as a pre-treatment before a tar or copper-based dressing is worth doing. As a standalone treatment for rope in seawater, the trials are clear enough that I would not rely on it.

Aluminium stearate

Aluminium stearate sits at the intersection of the rope and canvas series — the canvas post covers its waterproofing chemistry in detail. The question for rope specifically is whether a compound used primarily as a fabric waterproofer has any useful role on fibre cordage.

The internal abrasion concern that sometimes comes up — whether deposited aluminium stearate could act as an abrasive within the rope bundle — is worth addressing directly. Aluminium stearate is a soft, waxy solid that melts around 117°C and deposits as a thin hydrophobic film when its solvent carrier evaporates. It does not form hard crystals within the fibre bundle the way sodium chloride does. Under normal conditions it acts as a lubricant rather than an abrasive.

What it does not do is provide meaningful bactericidal protection. Aluminium at the concentrations present in a stearate treatment has no significant toxicity to the cellulose-degrading bacteria responsible for rope decay. Applied as a sole treatment it will slow moisture uptake and reduce internal abrasion — both useful — without addressing the primary biological failure mechanism at all. As a supplementary waterproofing treatment for rope used predominantly in wet conditions without sustained immersion — jacklines, deck lashings, canvas-covered work — it has a legitimate place. For rope in sustained seawater contact, it is a useful addition to a tar or metal soap treatment, not a replacement for one.

Paraffin oil

Paraffin oil was used considerably in American rope care practice, recommended partly on safety grounds — it is not inflammable where petrol and benzene are. The Atkins and Purser trials tested it as a carrier for copper soap treatments directly, and the results were poor. Paraffin oil with copper oleate gave 10% retained strength against 56% for Coalite neutral oil with the same copper soap. Somewhat better for resinate than oleate, but still substantially inferior to the petroleum-fraction carriers.

The reason is penetration. Paraffin oil at room temperature has relatively high viscosity and limited affinity for cellulosic fibre surfaces. It sits on the surface rather than carrying the active compound into the rope body. The safety advantage is real. The performance disadvantage is also real. Atkins is direct: "To use paraffin is a very false economy." On the basis of the trials I agree, though the inflammability argument for petrol-based carriers is not trivial either, particularly when treating rope in enclosed spaces or in cold weather when ventilation is reduced.

The metal soaps

The copper soaps — copper oleate, copper naphthenate — and the iron soap that forms the basis of the DIY preservative approach in this series are the highest performers in the trials, particularly in combination with tar carriers. Copper naphthenate in light coal tar or Coalite tar maintained retained strength above 70% after ten months in contaminated seawater against zero for untreated controls.

The mechanism is direct biocidal toxicity: copper ions are lethal to cellulase-producing bacteria at very low concentrations, and the organic salt form carries them into the fibre structure where they remain active over time. Copper naphthenate is also a good lubricant — the naphthenate and oleate forms address both the biocidal and lubricant requirements simultaneously, which the trials results reflect. Copper resinate, by contrast, is a dry powder with no lubricant action, and its lack of lubricant function is a genuine practical disadvantage alongside its adequate biocidal performance.

The ecological position of copper in marine environments is serious enough that it warrants more than a footnote. Copper is a potent aquatic biocide, toxic to algae, molluscs, and crustaceans at low concentrations. It accumulates in sediments near treated structures. The eco-safety comparison post addresses this in detail. The iron-based alternative has a considerably more defensible environmental profile — iron is an essential marine micronutrient rather than a biocide at the concentrations involved — and the DIY iron naphthenate approach is what I use where a metal soap treatment is warranted.

Zinc naphthenate — colourless Cuprinol — performed poorly in the trials: 33–44% retained strength against 62–79% for the copper naphthenate formulation under comparable conditions. Zinc accumulates in marina sediments and is toxic to aquatic invertebrates and algae. It combines mediocre performance with real ecological concerns. There is no compelling reason to reach for it.

The practical hierarchy

Setting out a hierarchy feels more conclusive than the investigation warrants, so let me frame it as working conclusions rather than verdicts — these are the positions I have arrived at from the sources and from practice, and I hold them with varying degrees of confidence.

For standing rigging and rope that will be wormed, parcelled and served: Stockholm tar, applied by immersion into warmed tar, with iron or copper soap added if the rope will be in sustained seawater contact. Both the biocidal and lubricant functions are covered. The ecological case for iron over copper is clear from the trials and from the toxicity data, though the performance case is less settled — the trials did not directly compare iron and copper soap combinations under equivalent conditions, and I have not done so either. That comparison is on the list.

For running rigging handled daily: heat-bodied linseed oil as the primary dressing, applied warm, with Stockholm tar for annual deep treatment. The linseed maintains suppleness and hand feel between tar treatments. A line dressed this way smells faintly of something between pine and warm oil — not unpleasant, and a reasonable indicator that the treatment is still present.

For rope used predominantly above water — lashings, decorative ropework, rope mats — beeswax or aluminium stearate as a waterproofing supplement, with cutch as a pre-treatment on cotton. These are maintenance dressings rather than preservation systems.

For fenders and coir rope: Stockholm tar or iron naphthenate in a light oil carrier, applied by immersion. Coir's low baseline durability makes the case for treatment more urgent, not less.

What does not work well enough to recommend as a primary treatment: cutch alone for anything in sustained seawater contact, paraffin oil as a carrier for copper treatments, zinc naphthenate for anything, and raw linseed oil as a standalone dressing. These positions rest on the trials more than on my own practice, and the trials have their limitations. But they are the best systematic evidence available, and I have not found reason to contradict them from what I have observed.

Sources: W.R.G. Atkins and J. Purser, The Preservation of Fibre Ropes for Use in Sea-Water, Journal of the Marine Biological Association of the United Kingdom (1936). H.A. McKenna, J.W.S. Hearle and N. O'Hear, Handbook of Fibre Rope Technology (Woodhead Publishing, 2004). Charles Bushell, The Rigger's Guide and Seaman's Assistant (Griffin & Co., 1874). W.R.G. Atkins, The Preservation of Fishing Nets by Treatment with Copper Soaps and Other Substances, Journal of the Marine Biological Association of the United Kingdom (1928).

At VAKA the dressing system for working rope follows the same logic as the hull finishing system — address the actual failure mechanisms rather than reaching for the nearest bottle marked "natural."

Plans at VAKA Boatplans | Full knowledge base at Field Notes