So, the afternoon started fine, added another drop of water to the glue in the jar as it had all been absorbed. Then we fired up the gas stove and brought the water close to boiling point.
That's when I put the jar of glue into the water.
Remembering first to remove the lid. You don't want it exploding when you heat it!! And when you finish, make sure to leave the lid off/loose until it cools. You don't want it imploding, or seizing the lid on with the vacuum. Here's a closer look, see how it's gone all liquid.
However, before getting on with the glueing I needed to take some precautions. So I put a sheet of greaseproof paper over the baseboard, and then glued some more greaseproof paper to the top boards I made.
And then left them all to dry.
But eventually I had to bite the bullet and start glueing. And I'm afraid there was no time to take pics as I went. I had one clean break and 4 splits to get glued. However, the method is straightforward enough... use small paintbrush and dip into the liquid glue, paint glue along split/wood to be joined. I applied glue from both sides, and worked the wood a little to draw as much as possible into the repair.
Then it was straight into the jig for clamping. And the clamping pressure comes from the loops of string you can see.
The secret is to tighten the loops like a Spanish Windlass. It's a very old woodworker's technique that can apply a LOT of pressure with remarkable control. I use a variation of the technique to glue broken headstocks and the only real problem is that it is incredibly easy to put too much pressure on the joint.
The wooden blocks are there to make sure that there is plenty of downward pressure to ensure that the back remains flat, as well as the cauls applying the sideways pressure to clamp the glue joints tight.
And now I am just waiting. Hide glue dries initially by gelling, and then by evaporation. With the baseboard and top plates, it will definitely need to be left for close to 24 hours to dry properly. And open, or rubbed, hide glue joints can dry fully in a few hours.
So, fingers crossed. Of the 5 joints required, 4 looked fine. But one was visibly gapping, although less than 1/2th a mm, and I couldn't tell how well it would close without giving it a go.
I'll have no idea whether or not I've been able to save the back until I remove it from the clamping jig tomorrow...