This http://www.vikingrune.com/2009/01/viking-swords-ulfberht-fakes/ has the steel coming from Afganistan and Iran.

on the Aristotle furnace idea where have these been found and from what time period do they date

Sure the Roman letters would not be typical to Vikings, however I don't think it can be dismissed that the Vikings played a significant role in the origin of these swords. The Ulfberht is primarily found in Scandinavia which suggest that the Vikings either forged them or bought them.
Though I don't find it unlikely that the Vikings didn't forge the blades themselves I find it extremely unlikely that the Vikings should somehow have stolen a large percentage of these swords from the Catholics, manufactured over a large time period. It seems like quite a stretch in my opinion. Also it is not like high quality steel is a common thing in the hands of Catholics at the time. The Ulfberht is a unique sword in Europe and it's only found in small quantities, other swords of this quality is simply not found.

The vikings were some of the most vigorous traders of the time and have a large record of objects from Central Asia, so that Vikings could have bought steel of high quality to Europe and perhaps have it forged by Frankish blacksmiths are quite possible I think.

Another thing to note is that crosses on Viking objects are not that uncommon and also Roman letters on Viking objects are not unique. However because of the date of the first Ulfberht swords, it would have been rare for sure.

In the poem 'Judith' which is in the same manuscript as where the Beowulf is written, there is the description of the beauty of Judith: ‘Iudiþ ides ælf-scínu’. Now this is Old English where BERHT is Old Saxon. scínu and berht are both having the meaning of beauty / beautyfull. ælf and vlf are almost identical. Unfortunatelly elf in Old Saxon is Elevan. And there is no text at all that combines elevan and berht. So it most likely it is still a combination of the Old Norse word ulf for wulf and the Old Saxon name for beauty. So the sword is of Wulfbeauty. Not impossible to think.

intermarriages of words as Niels Just Rasmussen is describing is in this case explainable even further by referring to Haakon the Good. Who was foster to the Saxon-desending King Athelstan and grew up at that court before becoming the king of Norway. Haakon could have had the means to set up the enormes trade with the Samanid dynasty. This is explained by Hanley en Feuerbach. It is estimated that the trade brought about 125.000.000 dirhams into Scandinavia agains only 125 Frankish coins during that particular era. And in the area of the Samanid dynasty it is known that they produced crucible steel in enormous numbers. Exactly the steel used to produce VLFBERHT swords. When Samanid dynasty collapsed, there are no new dirhams arriving in Scandinavia and the numbers of Frankish coins is growing. Thus showing that the trade routes change.

All of this is important to understand that Haakon the Good could have played a role in the intermariage of the word VLFBERHT. Since approx 10% of Norwegian swords were VLFBERHT swords, it seems that they were meant for the Norse elite. Most of the VLFBERHT swords found in Central Europe were found in Rivers but in smaller numbers then in Norwegian. Where almost all Norse swords are found in burials. So depositing in rivers must have been a different kind of ritual as burying. It could even be that the Norsemen themselves made the deposits as they have been known for moving far along a lot of the Central Europe rivers, just as they did over the Wolga to sail to the Arabic world. So it could very well have been a ritual to honor a lost warrior in battle. Since practically no other VLFBERHT swords were found in a different context in Central Europe then in rivers, it can be concluded that there was hardly any trade of these swords into the Frankish realm.

And why +VLFBERH+T? Instead of +VLFBERHT+? Nobody knows, but it could be to mystify the word even more and combing two words VLFBERHT and VLFBERH. Wulfbeauty and Wulfmountain. Perhaps the name of the (first) smithy?

The Institute for Inorganic Chemistry at the University of Hannover recently examined an Ulfberht-marked blade found in the Weser River in 2012. They analysed the metal and came to several conclusions.

The high level of manganese in the iron points to a European source and not a Middle Eastern or Indian one.

The level of arsenic is consistent with ores found in Germany.

The handle was made from a lead-tin alloy. The lead isotope in that alloy only exists in what was known as the Taunus region, an area between the Rhine, Hahn, and the Wetterau.

During this time, most of the Frankish craftsmen and artisans were based in monasteries. There were two monasteries in the Taunus region that had a long association with weaponsmithing - one at Lorsch and one at Fulda.

IMO this closes the matter until contrary evidence is produced. Based on this new study and the arguments in this thread, Ulfberht was a Frankish smith probably working out of either the Lorsch or Fulda monastery. Confirmation would require a few more Ulfberht swords being given the same analysis or a document stating that someone called Ulfberht lived in one of those monasteries during the time in question.

The Weser sword proofs nothing about the entire lot recovered VLFBERHT swords. It is a one off. Unfortunately, the owners of VLFBERHT swords are not very helpful in analyzing their swords.

So the question is now, how would Central Germany in the early middleages be able to make the quality steel as good as Central Asia's, India's and Shri Lanka's crucible steel? It is recovered that in these area's were 100.000s bars produced. This is in no way found in Central Germany. So it is very unlikely that Central Germany produced the numbers of steel needed for all those swords found all around Europe. If there would have been the knowledge to produce the steel in Central Germany, no doubt more excellent-steel-products would have been made. The fact that not all found swords in Europe have crucible-steel-quality demonstrates that the steel was produced elsewhere and considered a product for the elite.

VLF seems Old Norse
BERHT seems Old Saxon
As Niels explained, this can make perfectly sense in a world that had much contacts with Danelaw-England.
There is nothing Frankish about the word VLFBERHT.

There is also no trade-route known from Frankish area to Central Asia on a large scale known to obtain the steel. The number of Dirhams found in Frankisch area is just too small. Also there was hardly a trade-route visible from North Europe to Frankish area before 950 AD. Till 950 AD only 125 Frankish coins can be found in North Europe against 1.000.000's of Dirhams.

This is what I said: "The Weser sword proofs nothing about the entire lot".

So yes. It is evidence. But only for this one sword found in the Weser.

By the way, thanks for pointing to Pawel Kucypera and Jiri Hosek. More to read and perhaps to come back on "my beliefs".

How the Ballinderry sword come to be in Ireland? Well, what do you think yourself considering that it was found along with other Viking objects: a longbow, two spearheads, an axe head and a gaming board? Plus the sword being very wide, which is typical for Viking swords. That the sword was found in a bog points also to the rituals from Northern Europe.

At least you could say that It shows that Vikings used swords with Latin letter words on them.

It is presented here that "....HILTIPREHT, .. seems to connect to to a Norwegian craftsman of that name." But I am not so sure about that actually. Because, to make things more complicated as they already are with the combi Old Norse+Old Saxon for VLFBERHT; HILTIPREHT hides PREHT which is not a typo for BERHT, it is nothing less than genuine Old High German. Pointing to Central Germany. The Dutch borrowed this word and I can say in my own language "wat een prachtig zwaard": What a beautiful sword. And HILTI is also Old High German with the meaning of "to fight". This points in the direction of the Taunus mountains where it is believed where the Weser sword was made.

So...... The question is now: How did a Viking become the owner of a viking-type sword with a Old High German word on the hilt plus a Old Norse/Old Saxon word on the blade.

I must admit that all the facts considered it does not yet lead to the right place off manufacturing. It could even be that more than one smith was asked to make a sword as good as an VLFBERHT sword and knew what to do: get hold of either crucible steel from the east or produce it himself in a fashion that is hardly understood.

Any other views on this?

There is no evidence that any of the Ulfberht swords came from anywhere outside of Europe. Hyper-eutectoid steel is NOT crucible steel. We know it can be produced in a regular smelter.