@Curly green finger's (but posted here in case useful to anyone else). I purchased some RTV silicone (sets at room temperature).
Silicone comes in different softnesses. The scale used is called the Shore scale and for this we're talking about Shore A (there are other letters). I used a rating of 15. I wouldn't go any higher, suspect 10 or below is what the Abelo ones use. Also check tensile strength of it (so it doesn't fall apart at demoulding). Finally you need to choose youre setting/cure time, I didn't go for an ultra fast one.
I tried two objects. One, my primary aim, a pine cone (open), the other one of my childrens' toy animals using the residue mixture.
I used old jars as the casting container (something the object fits in without too much dead space around the edges). The object was fixed to the bottom of the jar using hot glue, the correct way up.
Having thoroughly mixed the two compounds I poured the silicone carefully over each object and succussed the jars to bring bubbles to the surface as I don't have a vacuum chamber. You can pop these with hot air but blowing seems to work too.
Once cured I broke the jars with a hammer and cleaned off the shards. I then demoulded.
Plastic toy worked very well and demoulded easily.
Pine cone not so much. It was a
pain to get out so whilst my mix supposedly didn't require demoulding compound, I will look into this in future. Dipping the cone in beeswax pre-casting might be effective but I need to try this.
I will try again over the next few weeks and let you know how I get on. If successful I can potentially offer custom moulds if anyone has something in mind.
Photos attached.