What is the best method to create icing shapes from a mould?

2 Types of Mould:

Polypropylene

Silicone

3 Types of Icing:

• Royal Icing (that has not been fully whipped)
• Fondant
• Butter icing

Royal Icing:

My royal icing was 1 large egg white and approximately 150g of icing sugar (powdered confectioners sugar if you're from America), I only whipped it for approximately 3 minutes so it was thickening up but was not the usual texture of royal icing and still poured - just.

I prepared my polypropylene mould using cake release spray, although, this isn't something I have ever used for my cakes so I am new to it. I sprayed it over the inside of the mould and then used a silicone pastry brush to ensure it went into all the crevasses.

Having poured the royal icing into the propylene mould and I am aware that some bubbles have formed, but, providing the royal icing will set - there is a consensus that it may not - I think it will be worth a second attempt but starting by pasting the mixture over the mould using a silicone pastry brush. If the mixture doesn't set all the way through perhaps this could be used to build up a hollow shell in the mould (akin to an easter egg). However I am worried that the icing may dry too brittle and break while been removed from the mould.

Fondant:

I have tried a fondant Christmas tree via a polypropylene mould before; it didn't end well. I didn't grease/oil the mould and I suspect this was my downfall as I couldn't release the dried icing from the mould.

The fondant was rolled into a crease free ball then pressed into the moulds. The polypropylene mould was again coated with the cake release spray.

As long as I can get the icing to release from the mould this could be a great way of producing multicoloured objects from a single mould. If this works I would also be tempted to have a go with gum paste, as this dries better it may well be more tolerant to been moulded.

Butter Icing:

I really don't think this will work, but thought I would try anyway.

I don't measure anything for my butter icing but in addition to the usual unsalted butter and icing sugar I do like to add a small dash of water to the mix. this makes it softer and more workable but also helps it set. My icing was left over from another project and, consequently, spent the night before this experiment in the fridge, after warming up to room temperature I piped it into the moulds using a plain, round nozzle, then I smoothed the tops using a small tapered palette knife.

The polypropylene mould was again coated with the cake release spray. The icing was also refrigerated  in the mould to help the release.

Results:

The royal icing was white, the fondant was bright yellow and the butter icing was a creamy yellow:

In the Moulds:

Out of the moulds:

Oh Dear!

The cake release spray worked a treat and none of the icing stuck to the polypropylene moulds, I wish I had also used it on the silicone moulds as some icing stuck.

So the royal icing really didn't set, accept for a crust approximately 2mm thick, it did however, if removed from the mould very carefully (I dropped 2 as they dislodged before I expected), retain it's shape - see the 3D rose at the top right. I did get some air bubbles trapped, and this has effected the details on the rose, but as mentioned before I think this could be avoidable. I'll leave my intact rose to dry and see how it gets on especially regarding handleability. I really think royal icing could be used, fully whipped, in the polypropylene mould, especially if built up in layers; although it would be a bit of an ordeal unless you were doing lots of moulds or had other tasks to fit in whilst the layers dried.

The fondant in the polypropylene moulds worked really well! I was very pleased with my results. I removed them the day after I filled the moulds so the icing was dry but not hard. I think the trick here was overfilling the moulds so you had a handle to lever them back out again with - and the cake release spray worked a treat. I think the problem with this icing in the silicone moulds was simply that I didn't grease/oil the moulds.

The butter icing in the silicone moulds worked far better than I expected; but in the polypropylene mould; as I expected, it just went squish!