Originally Posted by Bruno
Judging by the patina, as a reenactor smith, I would say that this sword is recently made, chemically rusted and then blackened with motor oil in the forge.
Just an instinctive, rule of thumb judgement.
That kind of black doesn't come from some museum grade compound like paraloid.
And the rusting is consistent with modern steel rusting, some granularity and a few welld efined craters.
Ancient steel would rust in a less defined manner in my experience, with depressions having soft sloping.
Not to mention the lack of pattern welding.
Also the pommel lobes are quite crude if compared to examples that can be seen on the web, being photographed in well known institutions.
I support Bruno's observation regarding the patina and how the process oxidation / rust is a slow long process that can be read when looking at oxidation by ageing.
Difference in oxidation on Viking swords often depends on where they where found. If they have been lying clay in a fresh water river. If they have been in a grave close to a salt water sea. How much oxygen and water has moved trough the excavation site. What type of dirt the sword is surrounded by and its density and chemical composition. Temperatures trough the centuries in combination with the above. Regardless of the above the process of oxidation on steel that is over 900 - 1300 years is the same. Oxidation might look a bit different depending on the circumstances the sword has rusted in.
The condition of the sword above is what should raise the most suspicion. This Excellent plus condition for a Viking sword. Although I will not dismiss it 100% but this is a above museum grade quality sword and that in it self is reason for suspicion.
I would have the steel carbon dated. Understanding of Metal surgery is a must if collecting early items.