Sifting and Preparing Bologna Chalk The
gesso base must be built layer by layer, with each application varying slightly in composition. Here's how to proceed:
Step 1: Sifting Bologna Chalk -
Why sift the chalk? Bologna chalk is a hygroscopic material that absorbs moisture over time, forming clumps. These must be removed before mixing with the glue solution, as dissolving clumps directly in the mixture is challenging.
- Sifting aerates the chalk, improving its wettability when mixed with the glue solution.
Step 2: Preparing the Gesso Mixture 1. Start with the same diluted
rabbit skin glue (“colletta”) used for sealing.
2. Gradually add the sifted chalk to the glue, allowing it to hydrate properly. Add small amounts at a time to ensure even mixing and avoid lumps.
Step 3: Applying Gesso Layers 1.
First Layer:
- Apply the initial gesso mixture evenly over the surface. Allow it to dry thoroughly.
2.
Subsequent Layers:
- Increase the amount of chalk in the mixture progressively for each new layer.
- Let each layer dry completely before adding the next.
3.
Final Sanding:
- Once all layers are applied and fully dried, sand the surface using
240-grit sandpaper.
- Aim for a smooth, compact, and soft finish, ready for the next steps.
Key Notes The preparation of the
gesso base is critical for achieving a flawless
water gilding finish. Take the necessary time for proper drying and ensure each layer is applied carefully to create a durable, even foundation.
Applying the Bole After completing the gesso base, the next step in
water gilding is applying the
bole. Here's how to proceed:
Step 1: Preparing the Bole Mixture - Combine
bole with warm rabbit skin glue (“colletta”) at a ratio of
300 g of bole per 1 kg of colletta, creating a brushable liquid.
-
What is bole? Bole is a natural clay that serves several important functions in the gilding process:
1.
Seals the gesso layer: Prevents the subsequent glue application from being fully absorbed.
2.
Provides a colored base: Enhances the appearance of the metal leaf:
-
Yellow: For a classic gold finish.
-
Red: For an antique gold effect.
-
Black: For silver.
3.
Burnishing layer: Can be polished with an agate stone for added brilliance.
4.
Adhesive property: Bole reactivates when moistened, becoming tacky to hold the metal leaf.
Step 2: Applying Bole Layers 1.
Application:
- Apply
2–3 coats of the bole mixture with a light, precise touch, ensuring even coverage over the sanded gesso base.
- Use a crosshatch technique (alternating brush directions) to achieve uniform results.
2.
Drying:
- Allow each coat to dry fully before applying the next.
3.
Optional Burnishing:
- Once dry, the bole can be polished with an
agate burnisher to enhance its smoothness and brilliance, preparing it for optimal gold leaf application.
Step 3: Preparing the Fish Glue - Like rabbit skin glue, fish glue should be soaked in cold water until swollen, then dissolved in warm water.
- Dilute at a ratio of
1 part fish glue to 10 parts water. This solution will be used later in the gilding process.
With these steps, the surface is now ready for the final stage: applying the gold leaf.