Virtual thesis uh...
I chatted with the "guy" (LOL I joke but he's great, also an awesome super-prized modeler, someone will have seen his martini's wwwwide cinquecento with TR engine and some cool full detail deltas) -ok sorry, on the answer- he heard nothing about the srink you meant but he decribed very well the way they used at Giugiaro's Italdesign (years ago before rapid proto): I'll report despite there're no news I guess:
- 1/10 Skeleton done by plywood sections with 20 mm offset
- Filled with synthetic clay, he said that they bought the product in UK
- Clay's surplus was cutted out and checked with Perspex negative shapes (zory I hve the word in ITA but I can't to find a tech. translation, the word is DIMA= negative section, the external transversal section)
(ok I guess they worked exatly like you until now LOL, the difference I guess is that the clay remain (almost) soft, and the secret in in the next step:
- Obviously also them needed an hard surface to play with: they used a laser pantograph (not a scanner) that milled down the model from a Bayer resin block.