Polispectral vs. Black Oxide

[Max Stone]

I recently picked up a new Spartan PS, with the Polispectral finish on the stainless steel. Not having heard of this finish before, I thought a little research was in order, and to compare it to the Black Oxide finish many of us are familiar with, used by Leatherman, Gerber and other multitool manufacturers.

Surface blackening
Stainless steel surfaces can be readily blackened by immersion in a molten salt bath of sodium dichromate. This practice, which is relatively simple to set up and operate, is widely used by the automotive industry to blacken stainless steel parts (such as windscreen wipers) and by manufacturers of stainless steel solar-collector panels.

The process, applicable to any stainless steel type, results in the development of a very thin, smooth, black oxide film on the surface of the steel. The film is normally dull black but can be brightened by the application of oils and waxes. It shows no tendency to age or lose colour in service. It is ductile, will not chip or peel and is resistant to heating, up to the normal scaling temperature of the stainless steel. A blackened stainless steel can be moderately deformed without harm and the film exhibits good resistance to abrasion. It may be removed by corrosion and particularly heavy abrasion.

The salt bath operates at approximately 400 °C and dip time (varying from 5 minutes to 30 minutes) is followed by washing with water. Solar panels achieve an ideal blackening in 5 minutes, whereas auto trim parts take about 30 minutes to acquire a deeper black colour.

Electrochemical colouring
It has long been known that stainless steel surfaces can be coloured by treatment in a hot solution containing chromic and sulphuric acids or in a hot alkaline solution containing oxidizing agents. Many trials were carried out for commercializing the processes but coloured film obtained in this way proved too soft and porous to give adequate wear and abrasion resistance.

The initial breakthrough in colouring stainless steel occurred in 1972, with a colouring method known as the Inco-process, which is based on the anodic electroless deposition of chromium oxide.

Several proprietary variations on this process for colouring stainless steel have since been developed (including INOX®-SPECTRAL used by Victorinox), involving immersing the material in a hot chromic-sulphuric acid solution and following this with a cathodic hardening treatment in another acid solution. It does not apply any additional layer containing pigments or other colouring agents which might impair the properties of stainless steel. The colouring process chemically thickens the passive chromium-oxide layer that gives stainless steel its corrosion resistance. The colours are produced by the interference that occurs as light waves pass through the transparent passive layer.

Austenitic stainless steel is particularly suited to this electrochemical or interference colouring process. The immersion time of the steel in the acid solution determines the thickness of the surface film, the light wave interference (or filtration) and the intense reflected colour effect – similar to the rainbow interference effect of soap or oil on a surface. The specific range of colour effects the film passes through (bronze, gold, red, purple, blue and green) corresponds to an increase in the film thickness from 0.02 μm to 0.36 μm. Ferritic stainless steels can only be coloured dark grey by this process.

Being colourless, the chromium oxide layer is not susceptible to fading by ultraviolet light and, as the colouring process does not involve pigments, fabrication can be carried out after treatment without the film cracking. In bending, for example, the inert film will thin at the bent edge, marginally reducing the depth of colour.

Colour can be applied uniformly or deliberately varied for a rainbow effect. There will be slight variations in colour and for larger surfaces, it is important to obtain samples that illustrate the range of colours. Because the colour depends on the way light is reflected through a transparent passive film, the angle at which the surface is viewed can change the apparent colour. For the same reason, curving or forming the panels will also change the apparent colour of the stainless steel.

As the passive surface film is transparent, the underlying substrate finish will influence the final appearance. For example, a dull finish will result in a subdued, matt colour while a mirror polish will give a brightly-coloured appearance. Unlike painted surfaces, the colour will not fade over time with exposure to sunlight. However, if the surface is damaged by scratching, fabrication or corrosion, it cannot be repaired.

The colour can also be removed by abrasion, so it should not be used where accidental or deliberate damage can occur, such as in a high-traffic area or where there are wind-blown abrasives. Pickling, etching and electropolishing will remove the coloured surface.

Since there are no pigments or colouring agents that might bleach or fade, coloured stainless steel has a long life in terms of environmental exposure. The colour will not fade when exposed to sunlight or weather. It is reported that there is no colour change in electrochemically coloured roof panels even after 30 years. Furthermore, the coloured surface does not crack or peel and will resist ageing.

A particular attraction of coloured stainless steel is that it appears to change colour under different lighting conditions and angles, in both artificial and natural light.

Coloured stainless steel cannot be repaired if scratched and is therefore best suited to applications where scratching and abrasion are relatively unlikely.

Full article here: https://www.imoa.info/download_files/stainless-steel/euroinox/ColouringStainlessSteel.pdf

[Thunderpants]

Basically, the witches throw an ordinary 12 euro Spartan in a cauldron; they recite some magic spells, and when the Spartan comes out it is suddenly worth 64 euros!
That's magic!

[Max Stone]

Basically, the witches throw an ordinary 12 euro Spartan in a cauldron; they recite some magic spells, and when the Spartan comes out it is suddenly worth 64 euros!
That's magic!

Basically   

I expect the cauldron is in another village so a few extra pfennigs had to be exchanged for the service...

[gerleatherberman]

Great read, Max! Thank you for taking the time to put it together. 

[Max Stone]

  makes it a little less mysterious...

[Sawl Goodman]

Thanks for the explanation, Max.

Here's an unboxing of black and white PS Spartans:
https://www.youtube.com/watch?v=v_PaaSzrtvo

You can't fault his enthusiasm!   They're really stylish knives.

What colour did you get, Max? I like the all black one, myself. I shudder at the thought of the first scratch, though...

[Max Stone]

Thanks Sawl. I got the black one. Keeping it in a little soft bag I had spare from another knife. Afraid that it will be a shelf queen, but I don’t care...it’s special enough to enjoy for the design and finish. Have eyes on the white scaled one, and there’s also now a very smart camo Spartan PS 

[Gath]

I Think RT spirit is a pretty neat idea, gives a special look but the risk of wear on the finish is rather low.

[Thunderpants]

I gave a brand new RT Swisstool Spirit to a nephew. Years passed before I saw it again. I couldn't believe what a mess it was. "I dropped it in the sand a couple of times and it's been kind of crappy since then," was his verdict.
Such a gorgeous slab of Swiss engineering, reduced to a knackered collection of dings, bumps and scratches on which the blunt, bent & abused tools were unwilling to deploy until you'd lost a fingernail or two.
A sad, sad sight!

[Max Stone]

That is a shame TP.    seems the RT Swisstool Spirit is one of the more collectible models made back in 2010.

[Mechanickal]

I know Ethrealicer EDCs a Spirit RT since they were available (2010).
Of I recall correctly, he mentioned only seeing some "snail-trails" depending on the angle of light.

So I do believe it's a strong coating when cared for correctly.

[Thunderpants]

I'm thinking of putting orange scales on my black-black Spartan.
It would certainly look pretty awesome. Sadly my only set of orange scales are glued quite firmly on a Mountaineer Lite and they'll probably stay there. Great colour! This with black blades? Yummy.

[Max Stone]

Would be amazing! Get one of those orange knife/Spartan combo packs to swap the scales?   

[gerleatherberman]

Got my first Polispectral SAK on the way. The 2019 Man on the Moon LE. 

Been looking forward to seeing the Polispectral in person since reading this thread.

[Max Stone]

Good one GLBM. 
It’s less impressive than the marketing bumf. More a shiny dark grey than the deep black we’re used to on BO tools. And the Polispectral aspect (different colors) is not at all apparent. It’s still nice, but just a little overrated imo. Just so you’re prepared to be underwhelmed 

[spudley112]

I'm thinking of putting orange scales on my black-black Spartan.
It would certainly look pretty awesome. Sadly my only set of orange scales are glued quite firmly on a Mountaineer Lite and they'll probably stay there. Great colour! This with black blades? Yummy.

(Image removed from quote.)

Yeah, the orange and black looks good together.

[kamakiri]

Great thread, Max!  Been subscribed since you first posted. Also prepared to be 'underwhelmed' on inbound knives.  I plan to use one out of curiosity.

And I love the black n orange knives...Not sure how much I'd fork over for a PS SwissChamp with the translucent orange (clear like on the 58mm not the 'back-painted' style on the Spartan).  Or even the solid bright orange on the 'Walter' knife, but with a black printed shield.

[Max Stone]

Thanks kamakiri 
I must agree that the premium is quite steep for PS. There’s certainly a cost for the treatment, and they probably have to divert parts off the line and get the work done in batches by a 3rd party.
I’ve been eyeing the orange Spartan/knife combo with a view of a possible switch, but I’ve got a few other SAKs on the radar first. 

[gerleatherberman]

Good one GLBM. 
It’s less impressive than the marketing bumf. More a shiny dark grey than the deep black we’re used to on BO tools. And the Polispectral aspect (different colors) is not at all apparent. It’s still nice, but just a little overrated imo. Just so you’re prepared to be underwhelmed 

Thank you much, Max!

Fortunately I would have bought the Moon SAK anyway, but a side effect is it'll be the first PS tool in my SAK stable. Good to know it isn't mind blowingly awesome ahead of time. Definitely a lot of money for a darkening of the toolset.

Thank you again for the great thread and research you did about it! Definitely not so "mysterious" and "amazing" as Vic would have us believe. Gotta love marketing hype.

[Max Stone]

Thank you GLBM 

[Mechanickal]

Hey GLBM, I just noticed a post on Facebook that says the coating on the Man On The Moon knife is different from the one on the Spartan PS models.
Just informing you

[gerleatherberman]

 

Thank you GLBM 

Hey GLBM, I just noticed a post on Facebook that says the coating on the Man On The Moon knife is different from the one on the Spartan PS models.
Just informing you

Thank you for the info, Nick!

Now I am even more excited to see the MOTM LE.

[kamakiri]

I haven't put much thought into it 'til today...but I don't think we'll ever see a PS SwissChamp. 

I think mostly because it would be difficult to assemble the tools with moving parts like scissors and pliers without any damage to the coating.  And it would also be impractical on tools like either saw.

So without scissor and plier options...lots of good thin models and any big models would be out.

I would buy a PS Passenger though...

[Aragorn]

Spartan PS 91mm plus scales, black accessories (mini screwdriver, toothpick, tweezers and pen)

[Max Stone]

Very nice Aragorn 

I guess you did a scale swap? How did you color the accessories?

[kamakiri]

(Image removed from quote.)

Spartan PS 91mm plus scales, black accessories (mini screwdriver, toothpick, tweezers and pen)

 

Very nice Aragorn!    Any pics while you had the scales off?

Now I gotta work up some courage to mod brand new knives...