Correcting the core

After face casting the model and producing a plaster mould covered in the previous blog, the face cast need to be further corrected to make a master mould. This blog entry will cover correcting to core ready for fibre glassing in the next blog entry.

Once the face cast is made from plaster it is important to ‘correct the core’ this means to make the face cast perfect. Therefore, rebalance the cast with clay so the face is level, any undercuts are blocked out with clay and keys and boarders are made ready to make a master mould.

The core is corrected so that the master mould produced is level, undercuts are removed for easy removal from the silicone shown in the next entry.

Figure 1 & 2

To start correcting the core, the face cast is placed on a board and clay is applied around the edges to balance the face cast out and make sure there are no under cuts where the master mould will get stuck when removing later. The clay used is a soft, water activated pottery clay called ‘buff clay’.

Figure 3 & 4

The clay is smoothed up to create a seamless edge with metal and rubber kidney tools in figures 5 and 6 below, The kidney tools are available from any pottery sculpting website such as Scarva from this webpage: https://www.scarva.com/SearchResults.aspx?Search=kidney. The tools are used to create a smooth clay and the correct angle to prevent under cuts. The metal kidney is used to remove excess clay and the rubber kidney is to smooth the clay up the plaster cast.

Figure 5 & 6

Figure 7 & 8

After using the kidney tools and when the clay around the face cast as neat as possible the clay is smoothed with water and a sponge, then the board and face is cleaned up ready for the border to be made.

Figure 9 & 10

A border using the same buff clay is made around the face cast leaving a couple of inches from the face to make room for the keys shown in figure 9 A border is used to hold the silicone when later making the master mould and create a base, the clay is smoothed to make sure there is no gaps for the silicone to leak from. Keys are attached in trapezium shapes on the sides of the border, this is done for later in the process, so the silicone jacket sits in the fibre glass shell without slipping round.

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Key words:

Under cuts – areas that are curved that can create a vacuum pressure lock

Figures:

Figure 1 - (Radfelder A, 2020) Apply clay around edges of face cast, York college

Figure 2 - (Radfelder A, 2020) Top view of face cast, York college

Figure 3 - (Radfelder A, 2020) More clay removed and cleaned up, York college

Figure 4 - (Radfelder A, 2020) Top view of smoothed face cast, York college

Figure 5 - (Scarva pottery tools, ND) Metal scraper kidney tool [Image : Internet] https://www.scarva.com/en/gb/Scarva-Tools-Metal-Scraper-Kidney-Palette---Small/m-1034.aspx [Accessed 3/11/20]

Figure 6 - (Cromartie, ND) Large Rubber kidney (Soft) [Image : Internet] https://www.cromartiehobbycraft.co.uk/Catalogue/Potters-Tools-and-Accessories/Rubber-Kidneys/Large-Rubber-Kidney-Soft-CH6055#.X7uxSc37RPY [Accessed 3/11/20]

Figure 7 - (Radfelder A, 2020) Cleaned up corrected core, York college

Figure 8 - (Radfelder A, 2020) Top view of finished corrected core, York college

Figure 9 - (Radfelder A, 2020) Clay boarder is applied, York college

Figure 10 - (Radfelder A, 2020) finished clay work ready for silicone, York college