This article “Casting Notes for Silver Lost Wax Casting” contains detailed notes of experiments done on silver lost wax casting.
Casting of silver can be fairly easy and these notes are the results of my experience through trial and error as well as instruction from an experienced jeweler and instructor.
Mark Ruby the instructor for the Fort Collins Senior Center was instrumental in helping with these notes and instructions.
The person that has helped me test and experiment with the different methods is Mary Jo Ziedler. We have made some mistakes and we have had our successes. Mary Jo and I have only performed investment and casting using centrifugal equipment.
My experience with vacuum casting has been with the help of Christen Gaylord. It was her equipment that was used in the experience with this method.
All of methods of centrifugal or vacuum casting that I have performed have been based upon the lost wax concept. This is where one makes a model of wax, suspends the wax in a plaster like media called investment, fires the invested flask until the wax has burned out and then cast molten silver by centrifugal force or poured to fill the voids that were once wax.
The first instruction I have is to read all of the instructions, recommendations and warnings of all of the equipment and products that one will be using. Believe it or not this was one of the biggest helps I encountered in my experiences
To start one need to have an exact copy of what one wants to be made of silver which usually is formed out of wax. There are many forms of casting wax that are available. There are sheet waxes that are great for thin flat pieces. There are waxes designed to be melted and drizzled over water for a very organic look. There are waxes that are used for injecting into molds.
Organic items can be used in place of the wax as well. In our experimenting we have had some very unique items that were created out of twigs, pine cones, leaves and other organic items.
Once the models have been made they are mounted on a wax column that channels the silver to the models. This item is called a sprue. The sprue is generally a wax rod that attaches to a rubber base that holds the metal flask. The rubber base is called a sprue base.
When constructing the sprue tree, care and thought must be given to the positioning of the items on the tree for casting. They should be positioned so they are down stream from the sprue button and that no uphill flows are required. Think of this as if you are filling the flask up with water. Are there any parts that there may be a bubble form and the water cannot flow into it easily?
Items that have a fine finish are best mounted with the fine finish side facing away from the sprue. At times small bubbles of air will form on the side facing down during the molding or investing process. The bubbles can mar the finish.
At this point one needs to weigh the completely assembled sprue and the models that have been attached to it. We need this weight later when calculating how much silver we need to melt in order to have a safe and accurate casting event.
Weigh the sprue assembly on a scale that can weigh in grams. Be sure to record this weight so it can easily be recalled later.
i.e. Flask #1 sprue assembly = 11 grams.
Assemble the flask by installing the sprue into the sprue base and installing the metal cylinder into the sprue base. The flask is ready for investing.
This has nothing to do with monetary investments. Investment is the plaster like powder that is used to fill the flask. Once the flask is filled and allowed to dry it is placed in a kiln and slowly heated up to 1350 degrees F over about an eight to nine hour period.
Proper mixing of the investment is critical to the over all quality of the final product. Initially we experimented with various methods of mixing and then we read the instructions. Wow, what a difference it made reading the instructions. Who would guess the manufacturer would be the expert on their product?
We use Kerr’s brand Satin Cast 20 investment and these instructions are for this product. (Note: these same instructions worked for the investment that is at the Senior Center.)
The manufacturer’s instructions are for a general amount and do not get very specific for the various sized flask. Using their measurements generally creates too much waste. Through experimentations and studying different books Mary Jo and I came up with a centrifugal casting ratio and measurement system that gets the investment mixture correct and with very little waste left over. I then took this system and through some experimentation came up the amounts for vacuum casting.
The following table has the levels of water that each flask should be filled to for the determination of the proper investment mixture.
This Table is for use with non-perforated flasks.
|For Centrifugal Casting||For Vacuum Casting|
|Flask Height||%||Water Level mm||%||Water Level mm|
|2 1/2″ / 63 mm||65%||41 mm||60%||38 mm|
|3″ / 76mm||62%||47 mm||58%||44 mm|
|3 1/2″ / 89 mm||60%||53 mm||55%||49 mm|
|4″ / 102 mm||60%||61 mm||55%||56 mm|
|5″ / 127 mm||60%||76 mm||55%||70 mm|
The ratio for the investment mixture is 2.5 grams of investment for each mille-liter of water. i.e. The water volume was 320 mille-liters. Multiply 320 mille-liters times 2.5 which equals 800 grams of investment. (Take the mille-liters of measured water X 2.5 = grams of investment needed.)
I like to let my flasks dry over night as a minimum. At the Senior Center we typically let them dry for a week.
Using a kiln and the manufacturer’s recommended burn out schedule the wax is melted out and all the residues are vaporized.
The best kiln setup for this is a programmable kiln controller. With a programmable kiln controller it is pretty much turn on the kiln, start the program and wait approximately 8 1/2 to 9 hours before checking for the completion of the final hour at 900 Degrees F to start the melting of the silver for the casting process.
If a non-programmable kiln controller is not available then one has to diligently attend the kiln and manually control the temperatures for the recommended amount of times. This can be a cumbersome process and tie one up for the whole burn out time period.
The burn out should be complete and the flasks are ready for casting.
|Wax weight =||_____||Grams|
|Flax height =||_____||mm|
|Water level needed =||_____||mm|
|Water measurement =||_____||ml|
|Investment needed =||_____||Grams|
|Pour water into rubber mixing bowl:||_____|
|Combine Water and Investment in rubber mixing bowl:||_____|
|Mix investment slurry for 3 minutes:||_____|
|Vacuum rubber mixing bowl for 20 seconds:||_____|
|Pour investment into flask:||_____|
|Vacuum flask for 60 to 90 seconds:||_____|
|Let it setup and mark flask for identification purposes:||_____|
Ganoksin is the worlds largest educational internet site for the jewelry, gemology and metals field. We also offer an online orchid community which has emerged from this project. Learn more