Investing

College of DuPage  Metals and Jewelry Design  Kamal                                                                                                                                          

Investing

 If you plan on continuing in Casting — Buy a respirator that is rated for silica. Remember that Investment is nasty stuff!  Please contribute $3.00 for the cost of the investment you are using. 

 Preparing the Wax

Procedure:

 

  1. Select a sprue base and flask that fit you pieces.  Try to get as many waxes on one tree as you can since our flask supply is limited.  The more pieces cast together, the less time spent casting.  You should have at least 1/4” space on all sides, 1/2” space between the waxes, and 1” space from the top. 
  2. Sprue up wax tree with the heaviest part of the wax toward the base.  Place waxes at an angle so bubbles can escape later.  Double check for any reverse flow areas in your pieces.  Metal does not like to flow backwards.  If there is an area that is thin, make sure it is supplied by a sprue.
  3. Take the tree off the base and weigh on gram scale.
  4. Write down this weight.
  5. Replace the wax tree on the base and paint the wax with de-bubble solution.  Let air dry.
  6. Place the flask carefully over the wax and fit snugly into base.  If your wax is near the top, tape paper ring above the flask to avoid spills.  Do not let investment set up more than an inch above the flask.
  7. Measure the amount of metal you will need:

 

For Sterling Silver:

                        Grams   x     11 =                      grams of Silver Shot (Casting Grain)

wax weight                  wax weigh factor

                                       (specific gravity)

There are 32 grams in an ounce — weigh out the amount of silver you will need for casting, label and save.

Note:  If you are casting in a metal other than silver, the numbers will be different.  See the chart at the end of this handout.  Also, this equation only works with casting wax.  For other plastics or natural materials, use the water displacement method. A general wax weigh factor number for natural objects is 18.

 

Procedure for Investing:

 

  1. Measure the size of your flask.  Use the chart to determine how many ml of water you will need.  Zero out the investment scale.  Keep water away from the investment bucket.  Note – water should be about 70 degrees F.  Hot water will shorten working time.
  2. Using graduated cylinder measure the water from the tap in ml (1 cc = 1 ml) and pour into a black bowl.  Place black bowl under the hood with the investment scale and make sure the hood is on.
  3. Place gloves on hands if you have sensitive skin.
  4. Measure investment according to the chart.  The amount of investment is roughly 1 and 1/2 the amount of the flask.  Weigh on oz. scale.  Close the investment bag and put the lid on the box.  Remember that 1 drop of water in the investment box will ruin the entire amount!
  5. Put paper or wide masking tape around rim of the flask to give more room on the top of the flask.
  6. Add investment to water and slowly stir with the hand (gloves).  Try not to add any more bubbles than you need to but slowly work the lumps out.  You now have 9 1/2 minutes until the investment sets up.  See chart on the next page.
  7. Mix by hand 3 1/2 minutes
  8. Vacuum investment in mixing bowl for 1 and 1/2 minutes not to exceed 2 minutes.  You could also use the vibrator to get the bubbles out at this point.  Make sure the vacuum machine has a vacuum – play with the lever until bubble sounds are strong and the dial goes up slowly.  Wipe base of Vacuum with wet sponge to make an air tight seal.
  9. If you have an intricate design, paint the investment into the detail work with a paintbrush.  Pour the investment into the flask – on the side like pouring a beer.
  10. Vacuum the investment in the flask for 1 1/2 minutes – no longer.  Do not walk away from the machine as the investment can rise, spill over and clog the machine!
  11. After 10 minutes, carve your initials, weight in metal, and note if burnout is NOT for wax.  Fill out the chart on the clipboard.  Take off the tape/paper and throw away.  Take off the sprue base, rinse and put away.  Re-trace the information on the flask in graphite (pencil) so it will be easier to read.
  12. Make sure that the bag inside the investment box is tightly shut.   Again, one drop of water could spoil the entire amount of investment. 

Wipe down all surfaces and the floor with a wet sponge.  Make sure there is no trace of the investment powder anywhere.   Never dump investment down the sink.  Landfill is the proper disposal for used investment.

*** Remember, if you leave your flask to be burned out with the tape and sprue bases still attached, it will NOT be loaded into the kiln for burnout.

Carve your initials into the top of the flask when the investment is frosted.  Re-trace your initials with graphite when the investment has dried.  Write down the amount of metal in grams needed for the cast and a symbol for metal type (Silver = AG,  Gold = AU, etc.).

 

Example:

                                                              KMK                           This tells me that it’s KMK’s flask

                                                            10 g AG                        and that she needs to get 10 g of

                                                                                                silver ready when she casts this flask.

 ***  Fill out the burn out chart on the clipboard and place your flask on the casting table in the marked area for the day that you will be here to cast

 Note:  If you cannot come to cast on the day that you have scheduled, make arrangements to have someone cast for you.  The flask must come right out of burnout to cast and there is a risk of ruining the mold if the flask is cooled and then re-heated.

   The information presented in this handout and lecture does not imply that safety precautions are not needed.  Adequate ventilation, safety eyewear and rubber gloves are still essential to safe studio practice utilizing these processes.  All materials must be kept out of the reach of children and Material Safety Data Sheets should be requested for all chemicals.  All of the materials that are mentioned in this handout could be hazardous to your health and others if improperly handled.

 

Material Safety Information: From the MSDS of Investment — Silica

 

“Prolonged exposure to respirable crystalline silica may cause chronic lung injury (silicosis).  Acute developing silicosis may occur in a short time in heavy exposure.  Silicosis is a form of disabling pulmonary fibrosis, which can be progressive and may lead to death.  The International Agency for Research on Cancer (IARC) reports limited evidence of the carcinogenicity of crystalline silica to humans.”

 

Some Metal Properties:                                                                              Melting          Wax Weight

             Temperature         Factor

Copper Based Alloys

(Cu)

Copper : Cu 100%

 

1981o F

 

 

  Brass: Cu 67%

 

      1724o F 8.5

 

 

 

 

Zinc 33%

 

 

 

 

 

Bronze: Cu 96%

 

1825o F 9.0

 

 

 

 

Tin 4%

 

 

 

 

Silver Based Alloys

(Ag)

Fine Silver

(.999)

 

Ag 100%

 

1762o F 10.5

 

 

Sterling Silver     

(.925)

Ag 92.5%

 

1640o F 10

 

 

 

Cu 7.5%

 

 

 

 

 

Gold Based Alloys

(Au)

Fine Gold (.999)  24 K

 

Au 100%

 

1945o F 19.3

 

 

22 K
Au 90%

 

 

17.7

 

 

 

Ag 6%

 

 

 

 

 

 

 

Cu 4%

 

 

 

 

 

18 K Yellow
Au 75%

 

1800o F 15.5

 

 

(.750) Ag 12.5%

 

 

 

 

 

 

 

Cu 12.5%

 

 

 

 

 

14 K Yellow
Au 58%

 

1625o F 14

 

 

(.585) Ag 25%

 

 

 

 

 

 

 

Cu 17%

 

 

 

 

 

14 K White
Au 58%

 

1700o F 14

 

 

 

 

Nickel

42%

 

 

 

 

 

14 K Rose
Au 58%

 

1749o F 14

 

 

 

Ag 10%

 

 

 

 

 

 

Cu 32%

 

 

 

 

 

 

 

 

 

 

 

 

  14 K Green Au 58%

 

1722o F 14

 

 

 

Ag 35%

 

 

 

 

 

 

Cu 7%

 

 

 

 

 

 

 

 

 

 

 

 

 

10 K Yellow
Au 42%

 

1665o F 12

 

 

 

Ag 12%

 

 

 

 

 

 

Cu 41%

 

 

 

 

 

 

Zinc 5%

 

 

 
               

Note:  Wax weight factor is an approximation of Specific gravity.  Alloys from different suppliers may vary in percentage of materials, base ingredients or melting temperatures.

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