PDA

View Full Version : Does polish/finish affect reactivity?



Patatas Bravas
06-13-2013, 09:49 PM
Moving this over from another thread (Mucho Bocho's Shig-lovers thread ;) )....

I recall from somewhere - can't remember where - something about this, that a maker was finishing off a knife in a certain way because it'd make the cladding less likely to rust. There are various ways to finish: kasumi polishing, finer, coarser, polishing along the length of the blade, going from spine to edge, 'misty' finish, mirror, leaving deeper grind marks, etc. I think the clip I saw showed the maker leaving lines running down from the spine to towards the edge, and I think there was a name for this. So, I'm wondering if others have heard something similar. Due to its finish, could one knife be more reactive than another despite being made with the same steel?

This came up in relation to the reactivity-rep of Shigefusa which, apparently, use the same carbon cladding steel as many other makers.

DevinT
06-13-2013, 10:02 PM
The coarser the finish the more reactive it is.

Hoss

Zwiefel
06-13-2013, 10:12 PM
Devin, do you understand any of the chemistry/metallurgy behind that? With my meager chemistry/metallurgy education, I would have guessed the only difference is surface area, which would only have a marginal effect on reactivity. Maybe polishing it changes the chemistry of the surface somehow, or leaves a layer of something on there protecting it?

ajhuff
06-13-2013, 10:14 PM
It's strictly surface area. There's no change in metallurgy or chemistry from polishing.


-AJ

Patatas Bravas
06-13-2013, 10:17 PM
Yeah, I'd thought of the surface area thing too. However, with one of my knives smoother polishing (less surface area) did make it less reactive, but with another it became more reactive. Opposite.

Also, in the clip I saw it seemed the maker was deliberately leaving a coarser finish to reduce rust. Would have thought it'd have the opposite effect.

GlassEye
06-14-2013, 01:17 AM
In my experience, a finer finish is less reactive.

danielomalley
06-14-2013, 01:54 AM
In general, I've also found that a finer finish is less reactive. Certain ways of accomplishing a finer finish also seem to have an effect. In my experience, a satin finish or a stone finish, even if brought to an extremely fine finish, is still more reactive than a buffed or burnished finish. The explanation I've been told for this is that stone finishes and satin finishes (from paper) leave the pores in the metal open (effectively increasing surface area and leaving areas that can absorb oils and acids into the steel), whereas a buffed or burnished finish has closed pores. I've certainly found the results to be true ... Devin, do you know if the explanation that I've been given is also true?

-daniel

Squilliam
06-14-2013, 02:00 AM
Ah yes Patatas I remember that video. They were talking about the fine scratches above the shinogi that we see on single bevel knives. I cannot understand their reasoning there.
The only thing I can think of is if it causes the iron there to act in a hydrophobic way, encouraging the moisture to run down and off that area rather than sit as small globules on the surface.

IMO the aggressiveness of the scratches also affects reactivity, not just particle size. Eg. If diamond and jnat particles of equal size scratch a knife, the diamond-created scratches will oxidase more rapidly.

Patatas Bravas
06-14-2013, 03:13 AM
You might be on to one or more things there, Jonathan. ;) I've since had a look to recall that video, but to no avail. Do you remember?

TB_London
06-14-2013, 03:20 AM
In general, I've also found that a finer finish is less reactive. Certain ways of accomplishing a finer finish also seem to have an effect. In my experience, a satin finish or a stone finish, even if brought to an extremely fine finish, is still more reactive than a buffed or burnished finish. The explanation I've been told for this is that stone finishes and satin finishes (from paper) leave the pores in the metal open (effectively increasing surface area and leaving areas that can absorb oils and acids into the steel), whereas a buffed or burnished finish has closed pores. I've certainly found the results to be true ... Devin, do you know if the explanation that I've been given is also true?

-daniel

More likely buffing leaves a waxy / greasy film behind from the carrier in the compound

Zwiefel
06-14-2013, 03:22 AM
More likely buffing leaves a waxy / greasy film behind from the carrier in the compound

Thats my hypothesis as well.

zitangy
06-14-2013, 04:06 AM
Curious for the answer too... can only postulate..

1) Surface area of the knife wld still the same as teh size is still the same isnt it?

2. Contact area( with food) will be increased on smoother finish (as the striations can't be seen for mirror polish) and hence possibly stiction issues

a) thus I suppose being smooth vs reactivity question, I can only guess that oxidizing agent from food it will slide off being more shiny and slippery and less grooves to stay in. basically less build up of oxidation ( liquid agents from food) that causes it to change color))

b) A wipe on the blade wld remove more oxidizing agent from the blade as there is less trapped in between the striations

MY limited observation is that polished metal should have less reactivity and also oxidation and the answer could be that it being shiny, liquids stays in their tiny bubbles and are easily displaced removed. leave it there long enough it, it will "eat" into it.

only guessing...

rgds
d

maxim
06-14-2013, 04:23 AM
I think that is exactly the reason !

More likely buffing leaves a waxy / greasy film behind from the carrier in the compound
Most of the knives that we get is actually buffed, thats why i also think they are less reactive.


I dont think it is so simple like coarser the finish the more reactive it is. Finish can be very coarse but still very buffed or mirrored

Justin0505
06-14-2013, 04:36 AM
its not just the surface area but how well the liquid can adhere to it. Think of frosted vs clear glass: how much harder is it to fully dry / wipe off frosted glass? Instead of beading up, the liquid disperses and sticks.

jai
06-14-2013, 10:55 AM
the deeper the scratches the more liquid can imbed its self into the steel so a smoother finish = less divits for moisture to get into the steel

maxim
06-14-2013, 10:59 AM
Unless those divits is highly buffed :)
the deeper the scratches the more liquid can imbed its self into the steel so a smoother finish = less divits for moisture to get into the steel

Zwiefel
06-14-2013, 11:23 AM
Unless those divits is highly buffed :)

Very silly! But funny. I'm imagining a tiny race of polishing bacteria, genetically engineered for jKnife maintenance. But there's a twist...you'll have to buy the book to find out.

DevinT
06-14-2013, 11:50 AM
Surface roughness also leads to more pitting because there are more sites for the pitting to occur. Corrosion is an electrochemical reaction so pits create a potential gradient and speed up corrosion. You can think of a rough surface finish as already having small pits just waiting for corrosion.

Larrin
06-14-2013, 11:51 AM
Sorry the post above was from me. I'm visiting Panaca right now and didn't switch over.

maxim
06-14-2013, 12:57 PM
I have seen some knives that was near mirror polish where scratches is super deep, long and very rough
Then also you see something like on jnat finish where scratches super short and shallow but surface look very sandblasted.

I will bet that this sandblasted super fine finish catch much more water then rough mirror buffed finish

Very silly! But funny. I'm imagining a tiny race of polishing bacteria, genetically engineered for jKnife maintenance. But there's a twist...you'll have to buy the book to find out.

zitangy
06-14-2013, 01:13 PM
I think that is exactly the reason !

Most of the knives that we get is actually buffed, thats why i also think they are less reactive.


I dont think it is so simple like coarser the finish the more reactive it is. Finish can be very coarse but still very buffed or mirrored

Interesting...

a) Not the typical home user to have a wheel for polishing and or buffing and compounds. Maybe a serious knife knut or a DIY person. Thus we can assume that its done by hand and sandpaper or stone most of the time.

b) Even if so, isn't it a common practice to wash off the blade with soap after polishing and buffering and hence removal of wax from the compound? Having said that.. some soaps still leaves a thin film residue..

c) From the factory... it has to look good adn pristine adn they will do what it takes to let the customer have a nice feeling after spending the money. It is for this reason that I wash all new things for the kitchen with mild detergent adn hot water .

still :scratchhead:

hv a nice week-end..
d

ajhuff
06-14-2013, 03:50 PM
Moving this over from another thread (Mucho Bocho's Shig-lovers thread ;) )....

I recall from somewhere - can't remember where - something about this, that a maker was finishing off a knife in a certain way because it'd make the cladding less likely to rust. There are various ways to finish: kasumi polishing, finer, coarser, polishing along the length of the blade, going from spine to edge, 'misty' finish, mirror, leaving deeper grind marks, etc. I think the clip I saw showed the maker leaving lines running down from the spine to towards the edge, and I think there was a name for this. So, I'm wondering if others have heard something similar. Due to its finish, could one knife be more reactive than another despite being made with the same steel?

This came up in relation to the reactivity-rep of Shigefusa which, apparently, use the same carbon cladding steel as many other makers.

I don't think it was a video. I think you are referring to this post (http://www.kitchenknifeforums.com/showthread.php/12605-Janpanese-Bladesmiths-an-article-on-blade-smithing-in-Sakai?p=213203&highlight=#post213203), the first link, near the end it is referred to as metoshi. As Larrin pointed out above regarding corrosion being an electrochemical reaction, the science doesn't back up this description of metoshi. That doesn't mean it is not believed.

I'm not sure if reactivity to food and susceptibility to corrosion are necessarily the same.

Also, you mention cladding. Mild steel and wrought iron are not the same. So perhaps a difference you perceive is in two different materials thought to be the same.

-AJ

wsfarrell
06-14-2013, 03:59 PM
Here's the video referred to. The relevant point occurs at 2:55.

https://www.youtube.com/watch?v=iCtx8VYxUK4&feature=player_detailpage#t=176s

Patatas Bravas
06-14-2013, 04:28 PM
That could be it - around 2.50. The clip doesn't show up for me, so I'll re-post.


http://www.youtube.com/embed/iCtx8VYxUK4