Does Superblue 'patina' help prevent more serious 'pitting' later?

[nuubee]

I don't have any SB yet, but I will probably get an SB Stretch. Does working on getting a patina all over the blade protect it from more serious 'rust pitting' later, or is it mainly for the visual look? Thanks!

[mattman]

I don't have any personal experience, but, from what I've read, the answer seems to be "Yes, to an extent.", sort of like anodizing aluminum, installing a "good" oxidation later, before a bad one can take hold...

[kbuzbee]

I don't have any personal experience, but, from what I've read, the answer seems to be "Yes, to an extent.", sort of like anodizing aluminum, installing a "good" oxidation later, before a bad one can take hold...

True, but remember these new SBs are clad in stainless, so, Nuubee, you won't get a patina 'all over the blade'

Ken

[Holland]

helps a bit for sure, but as Ken said, all the FRN superblue sprints are laminated so it wont patina across the whole blade.

[JNewell]

I'm not sure it helps. Read this post from Cliff Stamp from BF - the black oxide he's talking about sounds a lot like what people do with mustard, vinegar and some food products:

Both of them are oxides of iron. They type which is commonly called rust is orange (Fe2O3) which is harmful because it is a volume expansion and thus is flaky and tends to eat into steels. There is also Fe302 which is blackish and what is called a patina. It tends to form under more acidic conditions and will form a sort of coating which will thicken over time. However the black oxide can be severely damaging as well, it just depends on the steel and type of exposure. I have seen deep pitting of black rust on D2 and typical high carbon stainless.



No, the exposure time is too short. I have seen it on 5160 when sharpening on a belt sander because the heat will accelerate the reaction and I have seen it form in the few minutes from walking up from the basement with the still damp knife.

-Cliff

[mattman]

I'm not sure it helps. Read this post from Cliff Stamp from BF - the black oxide he's talking about sounds a lot like what people do with mustard, vinegar and some food products:

Interesting... I wonder what ingredient in the steel puts it on the "harms vs. "helps" side of the line?

I'm curious if this is the same "black oxide" that's often applied to fasteners as an inexpensive corrosion inhibitor? (i.e. sheetrock screws, automotive fasteners)

What are the "black oxide" Leathermen ( Leathermans?) using? TiNi?

[Cliff Stamp]

In general, forcing a patina on a blade with harsh acids is known to cause embrittlement in steels, it is not something you would want to do in an actual working blade. How much damage it does depends on the extent of the exposure, the nature of the acid and the temperature.

As for protection, it is a very weak coating when thin, over time, when formed naturally it will make a very thick black scale that is very resistant to being penetrated by the orange rust - but again this is very different than jamming a blade into heated acids.

[nuubee]

As for protection, it is a very weak coating when thin, over time, when formed naturally it will make a very thick black scale that is very resistant to being penetrated by the orange rust - but again this is very different than jamming a blade into heated acids.

Ah. To a non-metallurgist like me, that makes sense. 'Bluing' on a firearm (and before that, 'browning'), done with a hot chemical salt bath, was originally intended to be a 'protective' finish on bare steel, but it's easy for the salts from skin to start working it's way through it if they are not wiped off with an oily cloth. And as for thick black scale, I always wondered why some old wrought iron didn't show a speck of orange rust. Thank you for the info, and I was unaware that the SB Stretch was going to be a laminate. Even better!

[JNewell]

In general, forcing a patina on a blade with harsh acids is known to cause embrittlement in steels, it is not something you would want to do in an actual working blade. How much damage it does depends on the extent of the exposure, the nature of the acid and the temperature.

As for protection, it is a very weak coating when thin, over time, when formed naturally it will make a very thick black scale that is very resistant to being penetrated by the orange rust - but again this is very different than jamming a blade into heated acids.

Question: what would constitute "harsh acids"? Household vinegar? Or something stronger?

[Blerv]

I'll probably just regularly wipe it down with the Tuf-Cloth I use on the Superblue Caly3.

[GrossPolluter]

I'll probably just regularly wipe it down with the Tuf-Cloth I use on the Superblue Caly3.

do

[fanglekai]

I believe acids are a bad idea because of hydrogen embrittlement. If I want to form a patina I cut meat and fruit and let the juices sit for a minute or two before wiping it off. I doubt that would hurt the steel to any noticeable extent.

[dbcad]

I believe the blackish oxide is Fe3O4. Iron has a bunch of valence states though :)

The Mule in my ktchen has just a very little bit of Fe203, a couple of surface spot after a couple of years of use. I let the patina develop naturally and the entire suface area of the blade is a nice dark gray :) My suggestion is to not rush a patine on SB :) It develops nicely on it's own with a bit of use :)

Not the best pic, but the current state of my SB Mule. With common sense care rust shouldn't be a problem :)

[Cliff Stamp]

Question: what would constitute "harsh acids"? Household vinegar? Or something stronger?

Most of the research is on stronger acids and elevated temperatures, however room temperature embrittlement is known to be a problem and there have been some breaks in larger knives which seem to be so related. I would advise to err on the side of caution and just let it happen naturally - but it is your knife.The only thing I would advise to think about is the extreme effort which is made to make modern steels extremely pure, have very fine and consistent micro-structure - and how much sense does it make to jam such a material into even dilute acids.

[GTPowers]

Not the best pic, but the current state of my SB Mule. With common sense care rust shouldn't be a problem :)

Aaaaaaaaand I need to go change pants.

[Ed Schempp]

Anything that discolors the blade is generally some form of oxide, Cliff explains that concept well. The better patinas usually include something beside O2.

We did some experiments on 4 inch pieces of bandsaw blade in HCl at different heat treaments and states, annealed normalized, and hardened. This experiment was done in my shop not in a lab. Rather than vast amounts of empirical data we were just trying to get a feel for a difference in destructive testing. Daryl Meier, (One of my Icons) and several other astute smiths were conducting the experiment. We could not induce an effect that we could demonstrate. Maybe we didn't have the right alloys, temperatures or concentration, but the solution that we were using was the same solution that we use to descale damascus billets. We wanted to know if and how much we were effecting our billets.

I have several carbon steel knives in my kitchen. The stains change with the cleaning and the different pattern changes are a parallel of life, some stains are added some are cleaned away. The knife is a record of it past and not a bad thing.

Oxidation on a blade is basically just detrimental to the blade. Pits can cause weakness and lead to failure. Just keep it clean, stains will come and they will go...Take Care...Ed

[JNewell]

Thanks, Cliff and Ed. For clarity, I have never artificially aged / "patina-ed" / rusted any blade or other tool. I was taught very early to take care of my tools. I frankly don't understand the desire to abuse a tool to make it look aged or old or used other than through natural aging and use with proper care along the way.

Most of the research is on stronger acids and elevated temperatures, however room temperature embrittlement is known to be a problem and there have been some breaks in larger knives which seem to be so related. I would advise to err on the side of caution and just let it happen naturally - but it is your knife.The only thing I would advise to think about is the extreme effort which is made to make modern steels extremely pure, have very fine and consistent micro-structure - and how much sense does it make to jam such a material into even dilute acids.

Anything that discolors the blade is generally some form of oxide, Cliff explains that concept well. The better patinas usually include something beside O2.

We did some experiments on 4 inch pieces of bandsaw blade in HCl at different heat treaments and states, annealed normalized, and hardened. This experiment was done in my shop not in a lab. Rather than vast amounts of empirical data we were just trying to get a feel for a difference in destructive testing. Daryl Meier, (One of my Icons) and several other astute smiths were conducting the experiment. We could not induce an effect that we could demonstrate. Maybe we didn't have the right alloys, temperatures or concentration, but the solution that we were using was the same solution that we use to descale damascus billets. We wanted to know if and how much we were effecting our billets.

I have several carbon steel knives in my kitchen. The stains change with the cleaning and the different pattern changes are a parallel of life, some stains are added some are cleaned away. The knife is a record of it past and not a bad thing.

Oxidation on a blade is basically just detrimental to the blade. Pits can cause weakness and lead to failure. Just keep it clean, stains will come and they will go...Take Care...Ed