MeshPL - 12-3-2017 at 10:26
So I have a question. Stupid one.
Assume I have a large ball composed of water, cellulose and a bunch of other compounds (apple) embedded in plaster of paris. I was thinking, if it was
possible to dissolve the cellulose (apple) by subjecting it to conc. NaOH for a long enough time, while keeping the plaster mostly intact. Even month
is time I am able to wait.
If this would help, I could add an oxidant to the solution, for example: KMnO4 or H2O2. Or some other commonly available chemical.
Acidic solutions would likely dissolve plaster of paris so they are not an option.
I may actually make a small test if you don't know the answer, but I don't know if it is even worth wasting chemicals.
Any ideas guys?
[Edited on 12-3-2017 by MeshPL]
TheMrbunGee - 12-3-2017 at 11:53
I would just heat it up/ boil in water for a few hours! 
apple would get
saggy/soft and should be washable from the mold. this would be easier, I think, and no NaOH should be used..
But if You want - NaOH would slowly dissolve apple.
elementcollector1 - 12-3-2017 at 12:32
Plaster of Paris softens in water, and is then prone to cracking due to steam escaping from pores, so that's a no-go.
While CaSO4 is inert to NaOH to my best guess, a NaOH solution will do much the same as water to the poor mold.
Perhaps the other way around - try heating the mold, with the apple inside? It should soften. Depending on where your pour spout is, you might then be
able to manually scrape it out.
It sounds to me like you're using a 1-part mold, which is poor practice for this very reason. 2-part molds separated at the middle of the apple would
give you a much easier time.
MeshPL - 12-3-2017 at 14:11
I technically don't have the mold yet, (hence: "assume"), guess 2 part mold is the only option. Do you guys know best way to do this? Cut apple in
half and just make molds of 2 parts separately , than glue them together with some more plaster? I only wonder if it would withstand some higher
temperatures then... It might crack on the seal.
elementcollector1 - 12-3-2017 at 15:51
Mix Plaster of Paris so that it's akin to pancake batter (the apple will not sink, but instead retain the position of whatever you press it into).
Place apple halfway in.
Allow to cure.
Place lubricant (not sure what) on sides of mold around the apple.
Pour second half of mold.
Let cure.
Remove first half and then remove apple.
Allow insides to cure (they might still be slightly wet). Bake dry.
It might take a few tries before you get the consistency and timing right.
RogueRose - 12-3-2017 at 22:38
What about H2SO4? You say acid is out of the question? Plaster of Paris is made from reacting H2SO4 with Ca(OH)2 or CaCO3 of some other calcium
base. I see no reason it would further react with the plaster of paris which is CaSO4 and it is an acidic odixant.
MeshPL - 12-3-2017 at 23:08
Lubricant... petroleum jelly will be a good one for sure and is commonly available. Still worried about the putting the molds together, but will see
in the future. Maybe aside from connecting the halves with some plaster I will also connect them by wrapping around with some wire or sth.
Thanks for suggestions!
Very dilute H2SO4 has little effect on CaSO4, but as concentration of it goes up, the solubility increases due to formation of soluble calcium
bisulfate.
Tsjerk - 12-3-2017 at 23:47
Maybe ionic liquids? Makes the experiment much more interesting as well!
I think concentrated NaOH should also work though
Although the apple shouldn't be too wet for ionic liquids to work
[Edited on 13-3-2017 by Tsjerk]
Zyklon-A - 13-3-2017 at 00:42
The extra steps for a one-piece mold are worth it.
In a nutshell, this is the process I've adopted. Never done fruit before.
1: make a full silicone mold of the apple
2: cut the mold in half and remove apple
3: cast a wax apple in the mold, polish it etc.
4: invest the wax apple in your plaster of Paris (or whatever, I think phosphates are better)
5: bake the wax out of the new mold for some hours, couldn't give you a number honesty. (I do 20 minutes at ~1000°C, and that's for much smaller
molds)
6: cast it however you know how. An apple will be easy, gravity will be sufficient to fill any voids.
MeshPL - 13-3-2017 at 05:28
I knew about this 2 stage process , but I just wondered, if it was possible to avoid extra steps, which will likely decrease amount of detail and make
the process more time consuming... although apples are not vary detailed and I do have some time.