The Facts About Metal Finishing and a Safety Razor
With all the finishes in safety razors, I thought I would write a blog on the subject and talk a little about the different types, costs, benefits, and limitations of different finishes. The subject of surface finishing is a very extensive topic. This article would be too long to talk too in-depth about the subject. My intent is only to provide an overview of the processes so you can understand the topics and maybe ask the right questions. If you want to see more specifics, ping me, I will try to up-date this blog or do a follow-up on the subject in another blog...
I will also talk a little about some other decorative finishes. This subject is also very broad, for some this takes a lifetime to master, especially in high-end watchmaking.
Typically, stainless steel and other metals use a number of different standards to define the finish. The most common standards and measurements are DIM, ASTM, and Ra to name a few.
https://isofinishing.com/surface-roughness-in-manufacturing/
The term DIN is an acronym that stands for “Deutsches Institut für Normung” or “German institute for standardization”. ASTM is the US version and stands for American Society for Testing Materials (ASTM). Ra is another acronym for measuring a surface finish, it stands for “Roughness Average.”
The long and short of these standards is that they attempt to quantify the difference between the “peaks” and “valleys” of a surface. They all have their drawbacks. Often times, manufacturers in and out of the shaving market create their own standards. Measuring a surface finish is very difficult and expensive which leads to a subjective perspective of how smooth or polished a surface is?
For the rest of this article, I will reference the ASTM standard but I will also need to reference “Ra” on occasion as, for us, it is the clearest and most well defined for the average person, however, I will try to reference other industry standards such as “True #8 finish” or “Super #8 finish”. Here is a chart that shows Ra(Microns) vs the ASTM standard for perspective:
* Hairline is another term for a rougher “Brushed” or “Satin” finish. Chart source:
https://www.imoa.info/stainless-solutions/archive/31/Stainless-steel-mechanically-applied-finishes.php
The ASTM standard uses the following grades:
No. 1 and 2Finish
This finish refers to cold or hot rolled sheet and rod material i.e. pickled (remove scales) hardened, cold, or hot rolled. I should note here that the above material is the surface finish of the blanks we buy to machine our razors parts.
No. 3 Finish
A rough linear texture. Generally a 40-60 grit. There is no standard for a “Machine Finish,” but depending on the part or type of machining it could fall into grade 3. A Ra number might be a better gauge for a machine finish. A turned handle that was done in a lathe could be classified as having a “Machine Finish,” however some lathes can finish a surface very fine...closer to a No.4. A mill(base plates and caps) will generally have a more rougher(#3) finish than a lathe(handle - possibly #4). With a quick polish and no sanding, it is also often called a "Pittsburgh polish" producing shiny machine marks.
No. 4 Finish
Also known as a “Hairline finish” a linear texture but even finer, typically created with a 60-180 grit. Also known as a “Satin”(120 grit) or a “Sanitary”(180 grit) finish.
No. 6 Finish
Also a linear texture but even finer. A soft satin finish...grits 240-320 are used for this finish.
No. 7 Finish
To achieve this surface finish, sanding to a 600 grit and then a 1 step buff is applied. At this level, sanding lines can be easily seen…in other industries this finish is referred to as a “brush mirror” or “directional mirror” finish.
No. 8 Finish
Highly reflective finish, machine lines removed however the faintest of sand paper lines can be seen. To achieve this step sanding continues well above 600 grit...we use +2500 grit paper prior to multiple buffing steps.
Super No. 8 Finish
A true “Mirror Finish”! No machine lines, all sanding lines removed. A hip joint implant or a military mirror/lens of some kind would be polished to this level. A diamond compound in excess of 200K grit is used to achieve this finish...
The most polished finish is a Super No. 8 finish, however, this surface finish, often found in the medical, military, and aerospace industry, is especially expensive to produce. When we were just starting Carbon Shaving Co. I had the opportunity to meet and talk with a local company that polishes lenses for missiles in addition to medical devices...diamond paste, under a microscope, while holding the tolerances that are needed is used to accomplish these finishes.
The term "mirror" finish implies a perfect mirror finish on all surfaces, similar to a "Super No 8" finish...I have only seen this on medical implants and military applications and the cost to apply this finish is massive.
High Polish Finish On Carbon Shaving Safety Razors
Now as a designer, we have to grapple with these finishes and decide what is the best finish for a razor application and how best to describe our finish. We refer to our finish as a “High Polish Finish.” We use grits and diamond paste higher than 100K grit on some surfaces to achieve a No 8 or higher. We struggle to claim a “No.8” or a “Super No.8” finish on the entire Cx as some of our surfaces have machine lines(under the cap) that we still finish but keep in order to preserve the high tolerances of our “pinch design”, we also have some surfaces with a knurling pattern. We choose a “High Polish” finish to describe our Cx models, a common term used in jewelry and the watch making industry because we think it is the best quality for our razors and the best way to describe our finish.
Benefits of a "High Polish" finish include:
Corrosion Resistance
A smooth polished surface provides the best corrosion resistance. Crevices provide a starting point for corrosion to occur. A smooth surface is the most resistant to corrosion.
Easier to Clean
A smooth surface is easier to clean. The crevices on a machined or rough surface finish(High RA) can collect bacteria and germs. This provides more space for them to live and grow, especially in a humid environment.
Less Drag
A polished surface provides the least drag on a surface (skin), and a polished surface provides a slick surface.
https://pubmed.ncbi.nlm.nih.gov/11194050/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4969518/
Sometimes we employ a rough finish when we want the most adhesion. For example, when we are bonding stainless steel or titanium to our carbon fiber, we create a rough surface. We also add knurling to enhance grip on the handle.
Decorative Finishes on a Safety Razor
While the functional element would call for a complete polished surface, we also recognize the desire for the aesthetics to shine through. That leads us to the decorative finishes.
The material we use is of a premium nature, these materials are hard and require more time and effort to finish. Some of these metals include Titanium and the premium stainless steel grade of 316L, a far more superior quality stainless steel than the “free-machining” grade of 303 stainless steel (I talked about grades and material in an earlier blog post). By using premium metals we believe it gives us the opportunity to do more decorative finishes without compromising the needed corrosive resistance of our Cx razors. Some examples of these decorative finishes include:
Perlage Finish
Perlage means “pearl” in French. In the high-end watch industry, it is extensively used on the inside of watch cases. This finish is often used in the food and beer industry and can be done using an abrasive and a rotating applicator.
“2-Tone” Finish
We apply a fine etching to non-critical dimensions and surfaces such as the underside of the base plate or the handles. This contrasting surface finish is often used in show car engines. We bring the surfaces to a polished state and then apply a fine etching to darken the metal. We have done limited editions using this finish, the contrast of a polished surface with a finely etched plane provides a striking contrast.
“Satin” Finish
Aesthetically a nice finish but not as corrosive resistant as a polished surface or even a No. 7 finish. The crevices provide a place for dirt and bacteria to collect. It can take less time to apply vs a polished surface but also requires skill and craftsmanship to execute well. The light scratches that ultimately appear on a razor are less visible on this surface. This finish is not expensive to produce but does requir skill, it is the same as a No. 6 finish mentioned above. It requires a 1 step finishing process with 240-320 grit sand paper. Some manufacturers bead blast the surface and call it a "Satin" finish...very inexpensive to accomplish this.
"Diamond-Like Carbon" or "DLC" coatings
Often found in the luxury watch industry but also in the aerospace, performance car racing and other high tech industries. DLC coatings are slicker than a polished surface, approaching that, if not exceeding Teflon. DLC is significantly harder and more durable then Teflon. The surface is extremely hard. Carbon is the key element in this finish, the surface can be grey to black and is often used on Formula 1 crankshafts to improve wear and fuel efficiency. In the watch industry it used to prevent scratches. This surface finish will not hide or remove surface marks, a high polish finish is required, then a DLC coating to produce a smooth surface.
Damascus Finish
While not a finish, stainless Damascus has a very unique surface with high and low valleys. Although the true secret of making Damascus steel was lost to time, today the efforts continue with more enhanced and exotic materials including stainless steel. From a Ra perspective, this finish has a high Ra rating. What makes our Damascus unique, is we use a custom forged stainless Damascus made from both 304 and 316 grades stainless steel. We then carefully “etch” the material in acid, the acid attacks or erodes the 304 grade first creating 304 valleys and peaks of 316 revealing the forged Damascus pattern. We then finish the material carefully with numerous grades of grits followed by diamond pastes.
Other less costly and rougher finishes used in safety razors include:
“Stonewashed” Finish
This finish is created by tumbling a razor with pellets and a solution. Inexpensive, uniform and leaves a non-reflective, rough surface.
“Bead Blasted” Finish
Also known as sandblasted, this finish is inexpensive to apply vs any polished surface, it leaves a rough, uniform finish making the material more susceptible to corrosion, collection of bacteria and will provide more surface drag. Similar to our “2-Tone” finish...we never use this finish where skin and razor contact.
“Passivate” Finish
This is a widely used cleaning process for all grades of stainless steel. A citric or other acid is used to remove free iron (iron will rust) from the surface. It can also do a good job of brightening the surface. This process will leave a very thin protective layer on the surface. It will not lower the Ra or remove machine lines.
“Electropolish” Finish
Electropolishing is a process that makes stainless 30x more corrosion resistant than passivation, it also removes some surface imperfection more effectively...it is similar to passivating but more aggressive in removing free irons from the surface. It can’t be done in a small workshop as it is a very specialized, controlled process, with highly toxic acids. If the metal is electropolished it is also “passivated” however if a metal is “passivated” it is not “electropolished”. We electropolish some parts prior to final finishing, it is one of the most effective ways to polish threads and knurling.
https://www.ableelectropolishing.com/resources/passivation-vs-electropolishing/
Chrome Plating Finish
On a final note I can’t ignore chrome plating as a surface finish...very inexpensive to make and exceptionally smooth, close to a “Super No. 8” in terms of its smoothness, however, it has 2 major drawbacks that prevent us from using it:
Durability
The razor will not last. Typically these razors can be mass-produced and are cheap to cast and plate. At the core they are made from a less corrosive-resistant material vs stainless and then covered in a strong but brittle layer of chrome. As a result, when the razor is inevitably dropped, a crack will start in the brittle chrome material, and corrosion will penetrate this crack in the surface. Another weak point with chrome plating is that the threads which take a lot of wear..this wear causes cracks in the chrome, which will cause the threads to break off. This is where chrome plated razors usually fail...
Toxic
Chrome plating is a very toxic process to the individuals applying the plating and the environment. It is a highly regulated process in the USA and is toxic to the environment. It's one of the big reasons why it is typically done in China, India and 3rd world countries.
You can always tell a chrome plated razor, they all have rounded edges, its difficult(impossible) to chrome a tighter edge found in machined safety razors. Most recently I was shown a chrome-plated razor from a gentleman who had received it from his late father, unfortunately, his piece had broken off at the threads...it was sad, as he still kept it.
If you have any questions about the finish on a safety razor feel free to reach out here!
Excellent post, Sean!
I learned a lot here; very informative and enlightening.