The discussion centers on the phenomenon of enhanced water absorption in clay when placed in a sealed plastic bag submerged in a 5-gallon bucket of water, referred to as scenario D. Participants concluded that the increased pressure from the surrounding water in the bucket, combined with the sealed environment of the bag, facilitates more effective water infiltration into the clay compared to scenarios B and C, where the clay is either submerged directly in water or in a bag without external pressure. The role of density differences and potential chemical interactions, such as pH changes, were also highlighted as factors influencing the absorption process.
PREREQUISITESThis discussion is beneficial for potters, materials scientists, and anyone interested in the hydration processes of clay, as well as those exploring the effects of pressure and chemical interactions on water absorption in porous materials.
Why? The bag foil prevents/hinders transport.ImaginaryTango said:...when you say the bag prevents or slows some kind of exchange - but wouldn't it be that it allows or speeds up an exchange, not slowing it down?
Okay - just trying to straighten it out in my brain.A.T. said:Why? The bag foil prevents/hinders transport.
This sounds like the most likely hypothesis.jbriggs444 said:What about the possibility that capillary action is responsible?
By itself, capillary action will tend to draw water into the clay. This will tend to expel any entrained air. If the clay is entirely immersed, there is nowhere for the entrained air to go. It is trapped and will be under some pressure. At best, it can attempt to bubble out the top. But surface tension will resist bubble formation. If, on the other hand, the clay has a surface exposed to air, then the entrained air has an exit pathway. Capillary action can then fully displace the entrained air.
The plastic bag is helpful because it ensures that air inside the bag will reach 100% relative humidity. The exposed clay will not dry out.
I'm really glad you posted this and shared the quote from @jbriggs444. I did read his post, but maybe, since I was reading a lot of posts, I missed some details and that may be the answer (or the best one we can get without a lot of experiments).Dale said:This sounds like the most likely hypothesis.
It could be tested by comparing a bag with trapped air and a bag with all air removed. It would also be interesting if the bag without air got an air bubble from the air originally inside the clay.
I guess I took the diagram too literally then. In this case I agree with @Dale that the mechanism proposed by @jbriggs444 is quite likely. And it can be tested more easily than most of the other ideas.ImaginaryTango said:I fill the bag to almost cover the clay, but not completely.
As @jbriggs444 and others have noted I think this is the key.ImaginaryTango said:I fill the bag to almost cover the clay, but not completely. Now that this could be part of the issue, I realize I've never asked if any potters cover the clay with water. I'm pretty sure local "lore" is to partially fill the bag.
I would not recommend cross post.ImaginaryTango said:I see there are also chemistry forums here. Is there a way to cross post or maybe I should copy this post and put it in the chem sections? Or tag some people there and ask them to look here? I don't know how much of a crossover there is between sections.
Yes, and I will be testing it. However, due to my clay stock just about running out so I'll be getting more fresh clay, it'll be awhile before I can test it. I'm sure the thread will have petered out by then, but I'll come back and report what I find.A.T. said:I guess I took the diagram too literally then. In this case I agree with @Dale that the mechanism proposed by @jbriggs444 is quite likely. And it can be tested more easily than most of the other ideas.
I've been thinking about that. I took scuba lessons decades ago and remember that every 33', in salt water, pressure increases by 1 ATM - but the human body does not compress, since it's mostly water. Clay does not have as high a percentage of water as mammals do, but I've seen a piece lose 33% or more of its weight after the bisque firing. That (the way I do it) is a firing that heats up to 180°F and sits there for hours to make the loose water evaporate. Then it ramps up to get to the point of inversion, where the water that's bonded to silicon in the clay is released and the receptors in the silicon molecules are blocked or inverted (I'm not clear on just what happens), so the silicon won't bond with water anymore.Herman Trivilino said:The only thing I would add is a comment about the significance of the pressure from submerging the bag. It may seem a small pressure but that is a relative term. CPAP pressures, for example, are on the order of 10 cm of water. So submerging the bag to a depth of, say, 30 cm or more creates a large pressure by comparison. The highest CPAP pressure is 20 cm, or 25 cm for some CPAP machines.
Okay, thanks. Won't worry about it then.256bits said:I would not recommend cross post.
Most users can and do scan threads and will add relevant information as they deem fit.
Cross post will destroy continuity.