Hello.
I think to do that surfaces (plastic toys or material Sculptures-Statues), I mean glossy and uniforms surfaces may follow a series of generic steps that would be great if they could be included in a plugin/script with preview options.
I have followed some simple steps in the example that I show:

In all cases I have used a smoothing option to improve the pixceles (G'MIC Anisotropic smoothing for example) for opbtain smoothed surfaces without noise.
In the first two Imagens I applied some color retouching and most importantly, the G'MIC filter "Relief Light", which I think is most important in all this.
In the other transparent versions, it is necessary convert the image to grayscale after to smooth the image. Therefore it is important to normalize the gray tones to avoid very dark or very clear tones. To do this what I have done is create a new all gray layer and apply Bump Map. Although it would be better if someone finds a better way to normalize the tones without bump map. Then I applied the most important thing: the G'MIC "Relief Light" filter. You can also apply textures to emulate some frost or cracks in the ice. Then play with the opacity. Could also be applied some color with Colorize to get something like jelly/candy effect. Finally, on the bottom layer just behind transparent sculpture emulate light distortions (Ripples, Waves).
I saw that "lylejk" has achieved an excellent effect by making an ice sculpture in this thread:
viewtopic.php?f=11&t=3404
Maybe he could help by giving more details of the technique used.
It would be great to have a plugin that could do all this

Ice requires work (lots of different things and not necessarily applied in the same way or at all) Yafu. I nearly always start out with G'MIC's Gradient RGB which I desaturate (like it more then Gradient Norm). From there, the steps are more involved to the point that I won't do a tutorial on (i.e., maybe a 40 step processes. lol). Just have to play with texture blends as well (use a few ice textures) and also the Ice Fire Script-fu (well there was an update which it a little better called Icicle). and also like using blends of EyeCandy 3's Glass filter and on and on. After I get the ice sculpture close, I add Supernova as a spot light. Anyway, if a guru can automate a good ice sculpture process, then my hat's off to them, but I personally am not going to hold my breath. Started doing virtual ice sculptures 4 or 5 years ago and fine new tools, ways, flows that make it look more authentic, so it's a process that continues to be fluid Yafu, and like the tau, you have to find your own path to enlightenment and balance.

Have you checked the gimp registry for a similar plugin?

It is true lylejk. But I pretend a basic plugin to simplify the work. You could then work on that basic image obtained.
Rod, I could not find plugins to do what I want do. It is even hard to find tutorials to do similar things (GIMP and Photoshop). Many tutorials start from real textures images of materials (Ice, Metal) which is something I do not want. My aim is to first obtain a basic image of what would be a sculpture and then apply textures and colors.

Well good luck with your search and if you find a great pipeline give us a holler on how you did it.