This will be an incomplete post, as I arrived on site too late for the first installment of Thora Sharptooth's class, but as the cloth in progress was very similar to the construction of my string skirt, I feel I can muddle through that on my own.  Thora's page on the warp-weighted loom; if you're interested in Viking stuff at all, look at her filing cabinet.

Wadmal is apparently 2/2 twill from Iceland.  It's woven on a warp-weighted loom.  We all got to do a bit of the process.

When I got there, the loom (and Thora) looked like this:

See the narrow sticks at the top? They have been woven through the warp threads in 2/2 twill, counted to be the right arrangement.  This twill went like this: stick 1 was woven through in pairs.  Then stick 2 started with a 1, continued in pairs, and finished with a 1.  Stick 3 started with a pair, but the alternate pair to stick 1.  And stick 4 I think was the "default" shed, so no heddles were necessary.

So, what's going on here, is "knitting the heddles."  Heddles are the thread loops that, attached to each of several heddle bars (those closet rods flapping around), control which threads are raised, creating one of four different shed space combinations.  Obviously, the heddles make the pattern, so getting them right and evenly proportioned for tension aspects is important.

We each tried out knitting a few heddles.

One passed the spool of linen (in his hand) behind the pair of warp threads shown by the pattern rods, over the heddle rod, reached under the heddle rod for the thread "neck", stretched the neck out, twisted it 180 degrees, and passed the spool of thread through.  The stitch is very close to knitting.

(here's the pattern rods, as well as the top of the loom)

(the lower part of the loom)  Those uprights are there to help control the heddle rods, which tend to wobble on you when they're loose.  Especially now, in the knitting of the heddles, it's important to keep them stable, so they're lashed to the loom structure with thongs.

When you have your heddles knitted correctly, you can lift the heddle bar, and the pattern stick should drop out easily.

(a good view of the warp weights – can you see how they're bound up by the distribution of warp threads?  I've pondered about this a good deal, how do you manage to not fight the loom weights?  You regroup them for your pattern when you're done setting the structure.)

That thinner stick is the default shed rod, and it's showing us how the warp threads need to be redistributed amongst the weights so it can clear its shed properly.

Untying.

Redistributing, still 6 threads per weight, but a different 6.  Multiples of 12 seem to be useful for this loom, and apparently loomweights are frequently found in groups of 3.

She's ready to start weaving, but I missed a picture.  See the two horizontal threads running underneath the cluster of heddle bars?  Those chain the threads in pairs, and are an ad hoc "reed", which manages spacing of the cloth threads.  One is worked on the front part of the default shed, and the other is worked on the back.

She's holding a sword beater, which is primarly used to open the sheds better, and only used once in four picks to actually beat (very gently) the weft into place.  There's a pin beater too, with which one scallops the weft into position.

Pulling hard on heddle rod, and clearing shed with sword beater.

The weft scalloped into place.

Juggling the heddle rods is quite a trick – the first one just floats on top of the work as you work with the second and the third.  The fourth is so stiff, that you push it backwards, through the loom – you see the shed opening here.

When all four rows have been woven, then you go back to the first heddle rod's shed, and beat carefully into place.  If you beat so hard that you lift the weights, you will end up with a
weft-faced fabric.  Tabby has to be beaten every row, and hard.  But twill was very gentle.

Although the cloth we were weaving in the class was quite narrow, this loom can do 40" wide fabric – which is wider than I can weave comfortably on my 4-harness jack loom, and requires two people.  I've read speculation that looms could have easily been wider – this process is slow and deliberate, and I can now understand how it might be a two-person process.  Which would suggest to me that narrower fabrics found in extant garments would have been woven to a specific width, on purpose.