First, paint the glass ampoule with gesso. This helps to roughen the surface so that the modelling clay will hold better in the next step.
Next, knead the modelling clay well and then wrap it around the glass ampoule. The mass can gradually be modelled in pieces onto the glass. The mass should not be too thick and the modelling mass pieces must be well joined together. When the modelling mass has been well joined together and everything has been pressed down well, you can smooth the modelled surface as well as possible with a little water.
Then model the face. Join the edges well with the base. Here, use the modelling tools and water to bring everything nicely into shape. After the drying time, sand the surface (not a must, if needed) and apply painting base.