Is bagging a green bowl necessary after sealing end grain?
Just wanted to point out my experience on green bowl turning. Background about me: I am an engineer and I have always liked to challenge assumptions, so I have started experimenting with whether brown paper bagging rough turned bowls is necessary at all if the end grain has been sealed, and also if the drying rate changed in or out of the bag..
So my setup is turning ~16″ Sweet gum blanks. First time turning Sweet gum, read that the drying of such a “wet” green wood could be a challenge. I turned 4 bowls from the same section of tree, straight grain, some spalting, and about the center 1/3-1/2 of the tree was the dark brown versus the creamy colored wood. The diameters of the bowls came to ~15-17″, the depth of the bowls varied from 4-7″ deep. The sidewalls of two were about 3/4″ thick and the others were about 1-1 1/4″ thick.
After each bowl was rough turned I slapped AnchorSeal 2 on the end grain portions of the bowls inside and out. Stuck 3 in the big brown paper yard waste bags (no plastic layer in the bags) (1 bowl in each bag) and left them to dry in a spare room in my house. The other one (one of the thinner walled ones) I left out in the open, same room. I then weighed each bowl periodically and then calculated the amount of weight loss during the time between bowl weighings.
I live in Missouri the bowls were turned in late September, so my house has had some AC days, a few heating days, and some temperate days. I wish I recorded the humidity now too, but I will save that for another day..
So finally the cool stuff:
Sweet Gum is wet!!!!!!!!!!!!! I had water slinging everywhere, on me, needed windshield wipers on my face shield, In general I have lost over 1-1.5L (~1-1.5Qt) of water weight over the last few weeks in each bowl. The water loss was very rapid at first which you would expect at the beginning and then has since slowed down considerably. The thinner walled bowls have some small cracks in a couple of places, all of them at the endgrain sides of the bowl. It does appear that the bowls will come to equilibrium in maybe 1.5-2 months (just in time for Christmas, if nothing else cracks).
The most surprising result to me is the fact that the bagged bowls match up in water loss so far compared to the unbagged bowl based on days elapsed from turning them. This seems counter to what I have seen in vlogs, blogs, or read in articles about green wood bowl turning. Which tells me that maybe the bag does nothing when the endgrain is sealed (with AnchorSeal 2). I graphed everything below. The red circles are the unbagged bowl and the blue points are the bagged bowls. The vertical axis shows the difference in weight that was lost from the previous time it was measured. You can see that the blue(bagged) dots pretty much match up with the same time frame from the red(unbagged). Also interesting is how fast it was loosing water at the beginning of the drying. To put those ~-150g/day water loss, that is about a 1/2 cup per day. That has drastically slowed down since then. It will be interesting to determine an “equilbrium”. I had a smaller cherry bowl that I was tracking, to see if this test was even possible, and eventually the change in weight did eventually fluctuate around zero. If the image did not come through in the text, it should be found as an enclosure.
So what? To me, it means that if you seal the end grain on bowls, that placing them in a bag may not be needed. I am planning to check other wood species to see if the trend holds, and also try without sealing the end grain see what will happen from the water loss perspective. Your results may vary, but the devil is in the details. Again my setup: Sealed endgrain with AnchorSeal 2, yard waste bags had no plastic liner but 2 layers of the brown paper, and drying in a ~72 deg room in the house.