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Pâte de verre
LIULI Revives the Lost-Wax Casting Method
The lost-wax casting method is one technique used in glass art production. The refractory plaster mold essential for casting is obtained by heating and melting out the wax. Due to the softness and flexibility of wax, delicate textures, elaborate details and precise lines are able to be intricately carved into the wax model and eventually cast into the final sculpture. In the 19th century, French artists rediscovered this technique, which had been lost for over three thousand years, leading to the modern European glass art movement during the Art Nouveau period.
According to unearthed artifacts, it's evident that the ancient Chinese were already proficient in this technique during the Western Han Dynasty in China, but it was also lost in subsequent dynasties. In 1987, independent research and development by LIULI revived and reinvigorated this tradition, marking the beginning of a new artistic journey for Chinese glass art. Today, there are over a hundred liuli studios throughout mainland China, Taiwan, and Hong Kong that continue to use this technique.
The lost-wax casting method for glass is extremely complex, requiring at least twelve steps to complete a single piece. It's akin to a long-distance relay race, where craftsmen at each stage must contribute with passionate attention to detail, endurance, keen foresight of the finished piece, a deep understanding of artistic concepts, and technical mastery. Additionally, teamwork and collaboration are essential to produce liuli artworks successfully; otherwise, impurities, shrinkage, deformation, or even breakage might occur.
Under the leadership of Loretta Yang, the glass workshop has persevered for 37 years, ceaselessly learning and creating, even amidst setbacks and failures. They have diligently improved and expanded their knowledge, pushing the boundaries of complexity and precision in their work. They have demonstrated mastery over ornate details, glass transparency, color variation, utilization of patterns, and the scale of their creations, showcasing the beauty of culture on the contemporary stage of liuli art. As a result, LIULI has become a beacon of innovation in the world of glass, recognized globally for their leading-edge expertise in the lost-wax casting method.
LIULI’s 12 Steps of Lost-Wax Casting Method
1 Design and Sculpture
Inspired by the characteristics of the liuli, appropriate themes are conceived. After confirming a 2D drawing on paper, the next step involves creating a 3D sculpture using clay. Prior to sculpting, it's essential to anticipate the shrinkage ratio and potential problems that may arise during the firing process and make necessary adjustments to the model.
2 Silicone Molding
The clay sculpture cannot be preserved without drying out, so we must replicate it in a malleable resin that can be stored as a permanent prototype in the event that we want to reproduce that particular work, or in case an accident happens in the kiln. This way, we don’t need to start from scratch with clay.
Using a liquid silicone, we brush the mixture onto the clay model layer by layer, ensuring uniform thickness. However, we must allow each coating to dry, which typically takes around 30 minutes, before applying the next. Different designs require different layers; sometimes up to 7 layers are needed. Once the silicone coating is completed and fully dried, we peel off the coating from the clay and pour resin in the now empty space. After the resin hardens, we peel the silicone off again. We then refine and polish the resin positive until it is exactly what we hope to replicate in liuli.
Using the now perfected resin prototype, the above method is repeated to create a far more detailed silicone mold, which serves as the final template for wax casting.
3 Infusion of Molten Wax
The silicone is very soft, unable to stand by itself, making it prone to deformation when pouring in the wax. Therefore, an outer plaster mold is necessary to provide support. The high-temperature liquid wax is poured slowly and steadily into the silicone negative, ensuring that every detail is fully saturated by the wax. Different artworks require varying wax formulas, so the craftsmen must adjust the ratios based on their instinct and experience.
4 Shedding of Silicon Mold to Obtain the Wax Form
During the cooling and solidification phase of the high-temperature liquid wax, excessive thickness in the middle can lead to tension and shrinkage in the design. To counteract this, craftsmen periodically scoop out the thicker, uncured wax from the middle before placing the work back into the vacuum furnace to remove air pressure from within the wax positive.
Finally, after the wax model has hardened and cooled, the silicone is once again carefully peeled away. It's crucial to be patient during demolding, especially when dealing with fragile, small tips.
The continuous pouring of hot wax causes the silicone to lose elasticity, which deteriorates the quality of the wax casting. On average, a silicone mold can only withstand 20-30 wax castings before its condition declines.
5 Wax Form Refinement/Removing Imperfections
The wax pouring process often results in the formation of small air bubbles and visible seam lines where the silicone segments meet. Craftsmen employ fresh hot wax to fill any holes in the cooled model, polish away seam lines, and refine the sculptural details, ensuring that the wax positive retains the clarity of the resin prototype.
6 Coating the Wax Sculpture with Plaster to Form a Refractory Mold
Glass casting necessitates high-temperature firing, and the wax models (positives) must be further replicated into refractory plaster molds (negatives).
The wax sculpture is placed on a flat wooden board, surrounded by metal rings, similar to cake baking trays. Refractory plaster liquid is tipped into the rings, around the wax, cautiously avoiding directly pouring onto the artwork to prevent air bubbles.
The plaster’s formula was perfected through exhaustive experimentation during the early stages of Liuligongfang’s establishment. It withstands temperatures of nearly a thousand degrees Celsius, yet remains soft enough for easy removal after firing. The elaborate details on the interior of the plaster negative needs to be sturdy enough to withstand the pressure from the heavy molten glass without being crushed or damaged.
7 Removal of wax with steam-the essence of the “lost-wax” process
After waiting for the plaster mold to dry, it is placed into a steam kiln. High-temperature steam is used to melt the wax positive inside the plaster, allowing it to run out as a liquid. The plaster negative, once cleaned and dried with an air gun, becomes the final template containing the desired internal shape
8 Choosing Color/Kiln Firing
At a high of 1400°C, raw materials containing various metal oxides such as silica sand, aluminum oxide, calcium, and potassium are melted to produce liuli of different colors and shapes. Commonly, liuli resembles a thick plate, referred to as a "cullet." Depending on the requirements, the raw materials may also be ground into different sizes, becoming "blocks" or even "powder".
Before mixing all the materials, the raw liuli undergoes a thorough inspection to eliminate impurities and is weighed.
The heating sequence, which can affect how the melted liuli moves, fluctuates based on variations in color, size, or placement of the liuli. Influenced by past experience and creative intent, the craftsmen decides the stacking order and positions of the cullets to create the desired color fluidity.
9 Re-firing at 900 Degrees Celsius
After placing the raw liuli in the plaster mold, they are placed into the kiln. With the aid of computer-controlled temperature settings, the kiln follows specific heating and cooling procedures, typically reaching temperatures of about 900°C for casting. This temperature softens the liuli, allowing it to stream into all corners of the plaster negative. The heating program determines the direction of the colors and the formation of bubbles.
Subsequently, the cooling program returns the molten glass slowly to room temperature. This step is critical; if the cooling happens too rapidly, it causes the glass to crack.
The duration of firing varies depending on the size and complexity of the artwork. Smaller pieces may take as little as a week, while larger, intricate pieces call for over three months in the kiln.
10 Removal of Plaster Mold
Once the firing process is complete and the artwork has cooled, the plaster mold is removed. This step is comparable to excavating archaeological artifacts since the delicate liuli enclosed within the plaster, demands a high level of patience and precision, much like handling fragile archaeological finds.
11 Retouching of Details/Burnishing and Polishing
The cast liuli artwork still requires several practices to perfect it, including: cutting off the sprue, measuring height and levelness, coarse, medium, and fine grinding with different coefficient abrasives, further shaping with various diamond-tipped tools, and finally, polishing with rapidly rotating buffing wheels to achieve its glossy finish. This stage entails the utmost attention and resistance to pressure. Any accidental breakage due to excessive force would render all preceding steps futile, as it cannot be repaired.
12 Final Inspection/Etching of Serial Number/Packaging
A series of stringent quality inspection standards are applied, checking for scratches, hair pin fractures, or any remnants of plaster debris left inside. Ensuring tips are rounded to avoid sharp edges, we verify the intended visual contrasts (light to dark), and textural effects (glossy to matte) are achieved. If the inspection is passed, the year and limited-edition number are etched on the bottom of the artwork, officially marking it as a work of Liuligongfang.
