Alkaline Solution for darkening Stainless Steel blades?

[Legendary_Jarl]

I got a US army knife made by victorinox and it comes with a little paper that states the dark finish is achieved with an "alkaline" solution that produces a finish "harmless to the human and to the environment". Does anyone know what this 'alkaline solution' could possibly be?

 

[Wharn]

I believe it is black oxide, but I could be wrong.

Taken directly from Wikipedia:


Hot black oxide[12] for stainless steel is a mixture of caustic, oxidizing, and sulphur salts. It blackens 300 and 400 series and the precipitation-hardened 17-4 PH stainless steel alloys. The solution can be used on cast iron and mild low-carbon steel. The resulting finish complies with military specification MIL-DTL–13924D Class 4 and offers abrasion resistance. Black oxide finish is used on surgical instruments in light-intensive environments to reduce eye fatigue.

Room-temperature blackening[13] for stainless steel occurs by auto-catalytic reaction of copper-selenide depositing on the stainless-steel surface. It offers less abrasion resistance and the same corrosion protection as the hot blackening process. One application for room-temperature blackening is in architectural finishes (patina for stainless steel).

 

[Legendary_Jarl]

I believe it is black oxide, but I could be wrong.

Taken directly from Wikipedia:


Hot black oxide[12] for stainless steel is a mixture of caustic, oxidizing, and sulphur salts. It blackens 300 and 400 series and the precipitation-hardened 17-4 PH stainless steel alloys. The solution can be used on cast iron and mild low-carbon steel. The resulting finish complies with military specification MIL-DTL–13924D Class 4 and offers abrasion resistance. Black oxide finish is used on surgical instruments in light-intensive environments to reduce eye fatigue.

Room-temperature blackening[13] for stainless steel occurs by auto-catalytic reaction of copper-selenide depositing on the stainless-steel surface. It offers less abrasion resistance and the same corrosion protection as the hot blackening process. One application for room-temperature blackening is in architectural finishes (patina for stainless steel).

I certainly hope not because copper selenide is apparently quite toxic and harmful to the environment: https://pubchem.ncbi.nlm.nih.gov/compound/Copper-selenide-_Cu2Se

 

[Wharn]

I certainly hope not because copper selenide is apparently quite toxic and harmful to the environment: https://pubchem.ncbi.nlm.nih.gov/compound/Copper-selenide-_Cu2Se

It looks like that is true for the “cold” or “room temperature” black oxide. Anything that is military spec needs to be “hot black oxide”. Now the question is whether or not the “US Army knife” is true military spec. I would hope/assume so. Maybe someone more knowledge can chime in though.