As a bit of a preface, this is by no means going to show how to do a traditional stacked birch bark handle. Orien is going to cover that. I thought I'd do this one on how to make a solid chunk of stacked birch bark material that could then be worked more like the way you'd work stabilized wood.
Raw birch bark as received from Paul, front view. Note area of clean peel (white) compared to unpeeled grey surface. Prior to flattening, the entire surface was peeled (by hand and assisted with a sharp knife).
Raw bark back view.
Note areas of clean peel compared to darker areas. These areas had to be scraped down with a
sharp knife and sanded with a sanding block to get the crud off.
If you read other sources on the web (basketmaking sites etc...) they'll say that you shouldn't soak the bark or else it'll stain from the "orange" layer. Since we really don't care about the white surface looking perfectly white (we're only going to see it side-view) it really doesn't matter for our purposes. Soaking definitely helps make it easier to bend safely without cracking it (ignore if you're working "green" bark. This sample was dry.). It also helps loosen some of the material up for scraping/sanding. I soaked this bark overnight to get it to safely roll flat.
Sorry. No pictures of the scraping/peeling/sanding process. Honestly, it's pretty self explanatory. My only comment is that for handle making, the aesthetics of the surfaces aren't as important as making sure that both surfaces are clean and smooth. I used a vibratory hand sander with an 80 grit pad to really clan off the back side of some of the bark. The upper surfaces peeled pretty clean, and didn't really require sanding.
This is my really expensive and complicated (and patented I might add, so if you copy it, send me royalties off of each knife you sell) bark flattening system. The bark is wet, and between the two layers of plywood on the cast iron surface of my table saw. 3 bricks for weight, and you're good. I think the only requirements for this step are that you have flat surfaces to compress the bark, a heavy enough weight, and that the surfaces that the bark is in contact with be moisture absorbent, to suck the water out of the bark.
This is the flattened bark. It still has some curve to it, but this really doesn't matter for our purposes. I've marked out three "scales" in pencil. To make it easier to mark the large number of scales the same size, I've made a plywood form to serve as a stencil. This makes it a lot easier to negotiate around large cracks and voids in the bark, while still keeping the measurements of each piece exactly the same.
This is the pile of pieces that I'm going to use for the handle. This is probably just enough for one handle. I separated the pieces into "A" grade (no defects), and "B" grade (small cracks etc...). There were of course areas in the original material that I did not cut out rectangles from as there were pretty large defects in it. If I had free access to birch bark, I'd pass on using the "B" grade stuff, but we don't really have birch here in So. Cal., and this is the entirety of the usable material that I received from Paul (thanks for sending it from Canada!)
In this pic, in addition to my currently super messy workbench, you can see a bit of where I'm going with my "non-traditional" approach. The box to the left with the slit in it is going to hold my bark pieces, and the wooden plunger that you can see in the center bottom of the pic (gluing up in the quick clamp) is going to compress the bark pieces flat, and hopefully with the assistance of some resin, into a solid block.
If I had access to birch on a regular basis, I'd probably have made my "form" and plunger out of metal, so they'd be reusable. If you used a metal form, and put the bark pieces covered in resin in a plastic bag, you could press down one handle's worth of material, then just slide the bag of material out when the resin was cured, and start on the next one. I plan on this wooden form/plunger being disposable, and I'm more than likely going to end up cutting and sanding my material out of this form.
Here you can see most of my supplies assembled prior to mixing up the resin. I decided to go with a clear coat resin due to its long working time and low viscosity. I went with this particular brand because it was recommended by the folks at the store as being very comparable to the West Systems 105/209 resin/hardener that I like, at around 1/2 the cost. Also pictured, the bark scales in the wooden form, a cut down plunger (so it will fit in my "mycarta press"), disposable gloves, measuring cups, a disposable aluminum brownie pan (great for adding resin to the scales as well as keeping resin off of everything else), and the essential glass of iced tea. Not pictured: a bamboo skewer mixing stick and my fancy yogurt cup mixing cup.
This is my stack of scales with some resin poured over them. This actually worked pretty well, but I did separate each scale and apply some resin to make sure that there was a good amount between each scale.
Here you can see the form with scales and plunger in place compressed in my wooden press. I made this press for pressing homemade fabric "mycarta" (not "Micarta" because that's trademarked of course!). The brownie pan does a great job of keeping the resin overflow in place. This is just what I'm using because it's what I've got. Any large clamp or vise would work just as well.
Now you can see the logic of the slit in the wall of the form. Excess resin can vent through that without having to squeeze up and around the plunger.
Here's a closeup where you can see the resin soaked bark under pressure in the form.
And here's the finished product. It's not a solid hunk of plastic, but seems more like dense cork material. It seems to be held together pretty well, but I'm thinking that I probably still wouldn't trust it for a partial hidden tang as the resin seems to have had pretty good penetration, but not complete penetration. To combat this problem, it would be possible with the wooden form/plunger system to have clamped up the bark, and added a couple of screws or a bolt to keep the plunger depressed, removed it from the clamp, and popped the whole thing in a stabilizing chamber.
I think the main concern as far as strength goes would be lateral pressure. As such, this material should work for full tang (slab handled) knives, or the more traditional pass through hidden tang.
The 0.16 square meters of slabs made me a roughly 1" wide by 1.5" by 3.5" long block. I'd probably use maybe 1/3 more material to get a block a little over 4.5" long for your standard knife.