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Say I have a soft, possibly porous object. I want to coat it with a material,

  • Resistant to boiling water and some scraping
  • Not hazardous, at least after the coating
  • Largely transparent

The idea is to take, say, a fruit with the insides removed and to make a cup or a vase out of it.

Is there something I could buy or make at home for this?

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    $\begingroup$ "I need a material that does X" is off-topic. $\endgroup$ – Aesin Jan 6 '14 at 0:25
  • $\begingroup$ @Aesin, why is that? $\endgroup$ – Karolis Juodelė Jan 6 '14 at 2:05
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    $\begingroup$ @Aesin - I'm not certain that "I need a material that does X" is off-topic. Certainly, there is nothing in the help center center to forbid it. Other sites in the network may have explicitly or implicitly forbidden these types of questions, but I am not sure we have yet. $\endgroup$ – Ben Norris Jan 6 '14 at 13:35
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    $\begingroup$ @KarolisJuodelė - You'll note that I advocated on keeping the question open because we have not settled on a policy. However, our on-topic list centers on understanding of chemical phenomena with questions that may be useful to more than just the OP instead of "I need something to plaster my deck with that is wind, water, and ice resistant and that bird scat bounces right off of and I don't care what it is as long as I can buy it on the internet." This second type of question does not seek understanding, and its answers will only be useful to the OP and not to anyone else. $\endgroup$ – Ben Norris Jan 7 '14 at 14:46
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    $\begingroup$ I'm voting to close this question as off-topic because ‘I need a material for X is off-topic’ $\endgroup$ – Jan Oct 30 '15 at 17:30
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You could vacuform heated thin PET film over it. That would not stop biology.

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  • $\begingroup$ +1 for "that would not stop biology" - cutting off the oxygen supply to a fruit changes its metabolism, but many enzymatic processes will continue, as well as bacteria-caused decay. You will need to preserve the fruit first, and the usual methods (formaldehyde, dessication) are not suited to your purposes. $\endgroup$ – rumtscho Feb 5 '14 at 20:13
  • $\begingroup$ If recipients or children believe it is edible and it is not - by composition or history - that is a bad thing. One could give it a dose of Bitrex denatonium benzoate to keep it out of mouths. It overall seems like a bad path to pursue. Edible bouquets are no more sanitary than their handlers. $\endgroup$ – Uncle Al Feb 5 '14 at 22:14
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In my opinion this is a (at least) two steps process:

  1. Make the fruit's peel more durable.
  2. Coating the inner part of the object.

Make the fruit's peel more durable.

The conservation of fruit peels (seems strange but is true) is a well know problem in the field of restoration of contemporary art. Zoe Leonard "Strange Fruit (for David)" is the classical case of study about this topic.

enter image description here

Zoe Leonard after the death of a friends of hers begun to sews the peels and do with different material to recreate the original shape of the fruit. This work of course was very degradable so a German conservator Christian Scheidemann developed a method to treat the fruit peel to make them more durable. He used the Paraloid B72, a well know ethyl-methacrylate copolymer used in conservation of cultural heritage, under vacuum. I'm quoting from the link above:

Early on, her dealer, Paula Cooper, suggested the possibility of preservative intervention for the sculpture. Leonard was amenable and worked for two years with German conservator Christian Scheidemann to devise a way to arrest the decay of the fruit surfaces. After much testing, Scheidemann developed a solution that consisted of shock-freezing the pieces and then penetrating them with Paraloid B72 under vacuum. This solution was complicated by the need to protect the wires, threads, and other elements from the Paraloid B72; in other words, the piece presented the intricacies typical of any mixed-media work. But Scheidemann succeeded in this as well.

A generic more detailed research about food conservation can be found in this here.

Coating the inner part of the object

As other user stated generally plastic glasses and other for drinking are made of polystyrene, PET or polycarbonate. The third one is more durable and use for stuff used more times. However coat a cup or a vase with plastic on you own is quite dangerous (there are chances of poisoning if done in the wrong way) and expensive and difficult. If you don't use vacuum you should use blow molding over a mold of the interior of the fruit (so you have to make a first mold and then another "negative" mold) and the attach the treated peel in a second moment with some adhesive, very expensive process. I could go to a Murano glassmaker with your mold! In this case you can add a plastic or glass edge to your cup I don't think is very nice to drink from a plastic peel.

There is an alternative cheapest way, using Food Grade Silicone Mold Rubber this is probably what I would used you can find in internet a lot of types of silicone rubber that can fit your needs.

However I don't think you can later wash it in the dishwasher!

Edit

As stated Jaroslav Kotowski you can use even a more expensive epoxy resin however you should pay attention to use a food grade epoxy resin. Non food grade epoxy resin could be very toxic.

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This probably doesn't count as a real answer since the underlying technology isn't coating, but:

What is possible to turn deceased people and their organs into durable objects should (in principle) work for a pumpkin or a melon too.

The process of plastination, as used by Gunther von Hagens for his Body Worlds exhibitions involves the following steps:

  • dissection and embalming: cut the fruit open and remove the "flesh", soak with aqeous formaldehyde to stop decay

  • removal of soluble fats: place object in an acetone bath

  • impregnation: place object in a vacuum chamber (exsiccator) filled with a reactive polymer and apply vacuum

  • curing: depending on the polymer, apply visible or uv light to harden the object

Admittedly, this is more of a mind game, but it should work :)

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you can use epoxy resin. It is transparent, can be boiled, easy to use and obtainable.

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