Then I used 3 different clays from the same producer (Baillet, France) with 1. no grog / 2. a bit of grog / 3. very heavy grogged
air supply. I look at the weather forecast and when it says: dry, warm and a modearte wind, that's when I start a pit fire. I have a blow pipe for my chimney, looks a bit like a didgeridoo, and I use this to blow into the pit when I think I need more air. But normally we always have enough wind here in the hills (oftentime too much....).
I think the pit is working against your means of control. The black smudge marks are caused from incomplete combustion which is what the pit causes.
(thats kinda how charcoal is made) When charcoal has complete combusion its ash. To get the temps you want, you're going to use smaller wood,
maybe 1" to 3"...and they are going to have to be dry..(.I covered that in a burnishing post.) I think the larger pieces takes too much energy to burn resulting in the incomplete combustion. Besides, when you have vessels in the bottom of a pit and a log rolls down, the sides of the pits direct the wood onto your pottery. Its better for the fuel to roll off and away than onto. (A voice of experience) Wind causes complete combusion and works in your favor, both in markings and control. As for temperatures, incomplete combustion wil be cooler than an open fire. So you may want to try your experiments using the same clay body, same shapes, and different regulations in the structure of the pit. Deep v.s. shallow.
It is the temper that compensates for wind. Not enough causes cracks, right amount is perfect, and too much causes cracks. So you'll have to experiment on that level as well. For me, I use about a 35% to 55% mixture, maybe more if the clay is storebought and the discision of the right amount is determined
by drawing a wire tool thru and examining the particle drag.
I like the others, like the brown jar... The shape and design are similiar to the Northwestern USA Iroquois pottery.
Oh, rotten limbs seem to burn hotter than solid wood. I've talked a park into allowing me to pick up their fallen rotten limbs.
Good luck with your endevors...