Blue kurouchi and lacquer, what to do?

[Aidan]

I have a Kanetsune santoku which has a an attractive blue cladding on the blade, this appears lacquered over so it that looks like it was painted on. I have seen a similar finish on a Sakai Takayuki in the past.
is this safe for food preparation, or should I go about removing it (with acetone) as suggested elsewhere on the forums?

 

[dafox]

I always remove the lacquer protective coating on my knives before using them, I've not heard if using a knife with the coating is harmful to your health or not. If you do remove the lacquer it may remove some if the kurouchi/bluing finish. I just removed the lacquer from a CCK kurouchi cleaver today and the acetone removed some of the ku finish.

 

[Runner_up]

I believe the lacquer should be food safe - it will wear off on it's own eventually.

@dafox is correct that removing the lacquer will probably remove some of that blued KU finish.

 

[Corradobrit1]

Its odd they would lacquer the entire blade as Kurouchi is naturally protective against corrosion. Just remove the lacquer from the blade road and leave the rest to come off naturally.

 

[Runner_up]

^^ Not really , I've seen a lot of KU Jknives that get the lacquer over the KU. This is not "true" kurouchi in that it is done using gun bluing or similar chemical reaction. It is very easy to remove and generally not as durable . If I remember correctly my Murata was lacquered over the KU, and my Takeda classic AS definitely has a light lacquer coating over the KU as well, or did when new anyway.

 

[Corradobrit1]

^^ Not really , I've seen a lot of KU Jknives that get the lacquer over the KU. This is not "true" kurouchi in that it is done using gun bluing or similar chemical reaction. It is very easy to remove and generally not as durable . If I remember correctly my Murata was lacquered over the KU, and my Takeda classic AS definitely has a light lacquer coating over the KU as well, or did when new anyway.

That makes sense then, if its only a cosmetic Ku finish

 

[Runner_up]

That makes sense then, if its only a cosmetic Ku finish

Well the iron clad Takeda is certainly a forge scale KU finish. You can see the difference on the newer stainless clad ones where the finish is completely smooth and looks like it was painted on.

A chemical blued finish is still protective against corrosion (obviously a moot point for KU stainless knives, like the Denka's you and I like so much), so not really just cosmetics.

 

[Corradobrit1]

The 'shiny' finish on the Takeda could be from the pickling process rather than an applied chemical lacquer. TF can change its process to give a matte or shiny finish and I assume others can too.

 

[Aidan]

I removed the lacquer with acetone, I first tried petrol, and Brasso to no avail.
the finish underneath is not metal but possibly painted on? It’s a lovely colour but if this is done with gun bluing then I have to remove it completely, I am not happy with that as they use selenic acid, not food safe! Unfortunately it begins to come off in speckles, it would appear, see photos.
thank you for your replies above Appreciated.

 

[Aidan]

Probably have to reach for the nitromors next and or some fine wire wool

 

[inferno]

its probably from the ht oven. the color can vary depending on oxygen/nitrogen content in the oven atmosphere, soak time, alloy type, final oxide thickness etc etc etc.

 

[Matus]

Shiny kurouchi does not necessarily mean the knife is lacquered. What I can say that this 'kuriouchi' is not a forged finish, but some chemical was used to turn the steel black (like gun blue or such). As any form of surface finish it will tend to wear off (also 'real' kurouchi does). The knife does not look lacquered to me.

 

[Aidan]

Definitely had a lacquer coat which came off with acetone leaving a mat bluish “ kurouchi “ type covering. I took paint stripper to this and nothing came off so I assume it is part of the steel production process/ heat treat/ as suggested above.
I worked on this with very fine wire wool without much change. Ithen stood it in a coffe bath for 6 hour to force a patina! I hoped this would reinforce the bluing but it appears to have overwhelmed it.
I feel happier though, I was not sure what had created the bluing in the first place.

 

[inferno]

bluing is just a type of oxidation imo. usually quite thin.