# Communities > Modern-era Swords and Collecting Community > Modern Production Katanas >  Purple/blue marks on blade after oiling

## Ludford

Is it normal to get some purple or blue marks appearing on the blade a few hours after oiling? The look similar to the refraction you get on oil slicks so I thought it might just be oil.
But then I have a harmonica with the same kind of patterns and that's tarnish caused by skin acids.

So are these marks on the blade normal or not? They wipe off with a cloth and the blade returns to shiny after powdering and oiling so it might not be tarnish I don't know.

----------


## eirik.hansen

Go with your instinct Mr. Ludford.

----------


## Ludford

My instinct is I'm not sure.

----------


## eirik.hansen

You said you thought it might just be the oil, and I think so too, I have noticed the same on my swords.

----------


## A. Timp

It s just the oil, its also much more evident on mirror finishes. Nothing to worry about.

----------


## Robert Bugh

Using different oils will do this too. Some folks use gun oil some use choji oil for their blades. I have done/do both and can get these colors if I do a shabby job getting the old oil off (I used to over oil my blades,you only need a light sheen). I don't know if you've changed oils but that is one way to get them.

Bob Bugh

----------

