Lost wax Ceramic Shell
Bronze Casting - basic process over 5 days
Site design by John McKenna, last update December 2014, ©copyright of John McKenna sculpture Ltd
Welcome to the Studio, firstly an initial induction to foundry layout, some preliminary Health & Safety talk, a short Q & A session and your feasible expectations from the course. There are lots of processes and topics but dont worry if you cannot fully understand the processes outlined below, it becomes much more clear when we explain the process and as you physically undertake the process.
A4A Art for Architecture & JohnMcKenna Sculpture Ltd, High McGowanston Studio, Turnberry, Girvan, Ayrshire, Scotland KA26 9JT Tel 01655 332215 http://www.a4a.co.uk
DAY 1: Welcome, Introduction to the 5 day course, Waxworking
We move to the wax making section, where we discuss the nature and qualities of wax, risks in using it, melting procedures, handling wax and modelling tools. You will make a small wax sculpture that will eventually be your finished bronze piece. We discuss the differences between ceramic shell mould investments and traditional plaster/grog investments.
This is a direct modelling in wax technique and this exercise alleviates the need to make a mould. We would seek to finish the small waxwork by Monday Evening.
The waxwork will then be prepared for the shelling process, so you will attach its runner and riser spruing system and then degrease the wax, finally placing it in the drying cupboard overnight.
DAY 2: Ceramic Shelling procedure.
Day 2 starts with the shelling of the waxwork sculpture. The wax sculpture is checked over and weighed, then it is ready to be ceramic shell invested by dipping into a tank of ceramic slurry, coating the wax fully in a ceramic refractory ‘slip’. After the wax is dipped into the slurry, whilst it is still wet with slurry it is stuccoed, this forms the primary coat. This process involves sifting a refractory sand over the waxwork to coat it, then it is placed back in the drying room. Whilst drying there will be a slide presentation of the casting process from start to finish, this will give you a fuller picture of what will happen over the course duration.
During the day the waxwork will need to be dipped twice more leaving 4 hrs between each dip. With each subsequent dip the stucco sand used will increase in grain size.
In between dipping coats you will make a small simple relief mould using RTV silicon rubber moulding compound to see the process of moulding with this great moulding material.
DAY 3: Shelling & Workshop practices
Day 3 starts with the continuation of shelling of the waxwork sculpture, layers 4. 5.and 6. The sixth shell layer being the last one, leaving the shell to dry further overnight. In between the shelling processing you will undertake various Workshop practices and use of tools. You will practice lifting the crucible (cold) and the pouring procedure. The participants need to become acquainted with the team work involved in a pour, so these dry cold practice runs are of great use, then a hot bronze pour into an ingot putting the knowledge into practice. This pouring is not heavy work and a part of the course but any participant can just observe if they so wish, engaging as much as they want.
During the day you will also get the opportunity to create some test patina's on bronze. Handling some of these chemicals can be a hazard so proper use and safety precautions will be discussed. You will mix up the various chemicals to create the patina solutions and try out various application procedures to see the effects.
There will be time to discuss sourcing of bronze casting material, building small furnaces, melting bronze, burnout kilns and setting up a small foundry.
DAY 4: Dewaxing, Casting and Knockout
Day 4 begins with burning the wax cups out of the shells and then de-waxing the shells fully. This involves putting them in a burn out kiln to burn all carbon residue of wax out leaving a clean 'porcelain' like shell, with the void inside which was where the wax sculpture was. Once the shells are burned out they are examined prior to pouring. Any cracks in the shell can be repaired at this point. Then the shells are placed back into the kiln and are pre heated prior to pouring molten bronze into them. Preparations are now made to fire the lift out crucible furnace.
Prior to pouring we review our safety procedures and technique, you will don safety apparel and melt the bronze in a crucible. When ready each participant will pour bronze into their own shell mould. This pouring is not heavy work and a part of the course but any participant can just observe if they so wish.
When your casting has cooled down you will knock off the shell investment revealing your cast bronze, then you can cut off the runners and riser sprues ready for bead blasting clean.
DAY 5: Fettling, Beadblasting and Patina
Final Day 5 your casting will be blasted clean in a bead blasting cabinet. This gives you a clean bronze, then you will chase off and work over the areas on the casting that the sprues were attached to.
If required a tapped threaded hole can be put into the base of your sculpture to allow mounting to a wooden or stone plinth at a later date.
A final glass bead blasting will give your casting a satin sheen, which is also a good 'tooth' for patina chemicals to bond on to the bronze. Alternatively the bronze cast could be progressively polished at this point if desired, this though is a quite arduous task. If a patina colour is desired then you will draw on your Day 3 patina experiments, then wax thesurface to finish your bronze.
1. Practical work experience of a studio art foundry
2. The completion of a small bronze casting of your own
3. Basic waxwork and mouldmaking technique.
4. An insight into the work of a practicing artist/sculptor.
5. The opportunity to share in our knowledge and experience of sculpture gained over the years.
6. Hopefully a feeling of self worth, the pleasure that comes from success, whatever your level of experience.
7. A desire to do more, pursue knowledge and to take your own work forward.
OUR EXPECTATIONS: what we hope you would gain from the course