On the Astra SS and blade coating

[RobW]

After putting together a solid three-blade stash of Astra SP, 7OC blacks, and Feathers for the forseeable future, I decided to go back to my blade sampler and just try out a couple more blades before digging in for the long haul with the other three. I scavenged around the pack and found a couple of the Astra SS (Superior Stainless) blades to try out for a couple weeks. I knew I liked the SP (Superior Platinum), so let's try out the uncoated version and see what happens. Unfortunately, I only made it through 3 pretty rough shaves before binning the first one, and it's doubtful I'll give the 2nd blade a try right away. This blade seemed to skip a little during the 2nd shave, and it was more pronounced during the 3rd shave. It wasn't horrible, but I had quite a bit of irritation from the very first shave on.

I really had to stay on top of my technique to keep the blade angle correct and shave slow and steady with a stiff wrist. I've been at this about 6-7 months now and have been using the same razor (a Red Tip SS) for about 6 weeks consistently, so I'm pretty confident in my technique. Guess I've just found a blade I won't be buying in bulk...

My question is not so much "Have you had a similar experience?" but more about what types of metal coatings help to raise a blade from mediocre to good/great (ymmv)? I had similar problems with the 7OC green series (Super Stainless)...perhaps this is a problem of not having skin tough enough to deal with raw steel? Do I need to be on the look-out strictly for platinum- or chrome-plated blades in the future?

Thanks in advance for your thoughts and advice...

 

[swinub]

Awesome question, presumably the coatings are there for a reason. Subscribing to see what people think...

My 2 favourite blades so far both happen to be platinum-coated (Feather, Astra SP), but I haven't done e.g. an SS vs SP comparison.

 

[Haegar]

To my understanding, at least PTFE (=Teflon) and Platinum, and maybe a couple of other coatings as well are primarily there to not let the dirt stick to the edge, with the benefit that the blade only has to cut the stubbles that are sticking out of the skin, rather than first having to cut through particles of old stubbles and a dried old soap/skin-cells mixture before getting to the stubble to be felled. Further I imagine (and this is just a conjecture of mine!) that maybe some coatings fill in or smooth out the grinding marks from the honing process. None the less, both Astras (SS and SP) work fine for me and I only believe to notice a very slight difference between them.

 

[mblakele]

Coatings seem to have two purposes: to reduce force to cut (FTC) with something like PTFE, or to improve longevity with something like platinum-chrome.

Blade makers back in the 1960s concluded that uncoated stainless blades were too uncomfortable to compete with carbon steel blades: too much FTC, leading to pulling and tugging. So I would be surprised if any modern stainless blades are completely uncoated. But I do not have any of the Astra SS to look at, either.

 

[mblakele]

Pretty much every step of the process is indispensable to modern blade-making, at least up to the coatings and packaging: http://www.youtube.com/watch?v=e9PnTPIKd3g covers the approach used by Merkur, including a "chromium-based coating".

US3829969 from 1970 may be the original word on platinum-chrome coatings. Fischbein is listed as an inventor, just as with the early Gillette patents on PTFE coatings. According to the patent claims, the goal was to put a layer of chromium on top of the steel, to protect against corrosion and improve blade longevity. But chrome does not like to stick to the steel, while platinum will stick to both steel and chromium. So they coat the steel blade with platinum, then chrome, then PTFE. Or they coat the steel blade with a platinum-chrome alloy, then PTFE.

How much platinum would this use? US3829969 talks about a thickness of 10-40 nanometers, only at the edge. As an alloy it recommends no more than 30% platinum. Edges are about 43-mm long. Using some generous approximations, I reckon 1-oz of platinum would coat half a million blades. I think that is probably too conservative, and the right number might be a million or more. But $1500 per oz for half a million blades is just $3 per thousand, or 1/3 of a cent per blade. There would be some waste, but my calculations were also very liberal. So the extra material cost seems acceptable.

Now, none of this is to say that Astra SP blades have a platinum coating. But they say they do, and the cost structure seems plausible, so I find it easiest to believe them. It might seem odd that Astra Superior Stainless are often about the same price or a little more expensive than the Astra Superior Platinum blades, but that may not have anything to do with manufacturing costs.

Getting back to whether or not the Astra SS blades are coated, the "Superior" in both names suggests a PTFE coating, like "Super" and "Extra" in other brands. This image of a new Astra SP seems to show a PTFE coating, as a darker band near the edge. Any platinum-chrome would be underneath that, and probably difficult to spot anyway.

 

[RobW]

Epic post, mblakele, thank you!

 

[BayRhum]

Is it know for sure the difference between Astra SS and SP is only the lubricity coating?

I find Astra SS to be much harsher than SP. Used a SS today as it was all that was in my travel bag on a trip. Horrible shave.

 

[BayRhum]

I work in manufacturing too. Have so for decades. And I can tell you sometimes the design and manufacturing engineers are the last to know of deviations or problems in the process.

On the coating for Astra SP, I was wondering if it was, at the least, an advertised feature or something.