top of page

INVESTING A WAX PATTERN FOR BRONZE CASTING

​

This is the method used at the Eastern Kentucky University Department of Art and Design

(There are many other ways of investing.)

 

N.B. Investing works best if you use a team approach. Two people are the minimum needed, but three or four is much better.  YES, one person can do this, but it is really difficult!
These directions assume that you already have gated your wax sculpture/pattern.

A SIDE NOTE: The photographs used for illustration are taken from a number of different casting sessions. 

MATERIALS AND TOOLS


FLASK MATERIALS: chicken wire – roofing felt – duct tape – 22 gauge wire
FLASK TOOLS: measuring tape – scissors or mat knife – wire snips – diagonal wire cutter – pliers
INVESTING MATERIALS: plaster – sharp sand (play sand) – luto – water – 8 oz. foam cup - denatured alcohol
INVESTING TOOLS: bowl or bucket for mixing plaster - measuring buckets – holding buckets – mix bucket – mixer – putty knife – hammer – cold chisel – air blast - brush – diagonal wire cutter. Some of the major tools are shown here.  Others will be shown as the work progresses

The smiley face is a nice touch!

​

    

                            THE INITIALS

​

​

​

    

                     POURING CUP

​

​

​

​

 

VENT

​

                   TRAP

​

​

PROCEDURE


The investment material for this procedure is made from a mixture of #1 molding plaster (plaster of paris), sand (play sand from Lowe’s), luto (old investment that has been ground into a powder and sieved), and water. The ratio of materials is:
Plaster ----- 1 part
Sand ------- 2 parts
Luto -------- 2 parts
Water ----- 1 7/8 parts (a little less than 2 parts) 

​ A  visual example of investment proportions. >>>>>>>>>>>>>>>>>>>>>>>>>>>

STEPS

1. Hand mix a small batch of investment, and, using the foam cup, cast a block of investment. This will be used to support the pattern when pouring the investment.

2. Measure the height and width of your gated pattern. Add to the measurements 2 to 3 inches to the width (so the gated sculpture will have a wall sufficiently thick to protect it), and 3 ½ inches to the height (for the support block).

3. DO THE MATH!  Multiply the width times 3.14 (3 1/7th ), and add 6 inches for overlap. The result is the length of the pieces of chicken wire and roofing felt you’ll need to make your investment flask. The flask’s height is the same as the pattern plus 3 ½ inches for the cup.

4. Cut out pieces of chicken wire and roofing felt to the dimensions you’ve calculated.

5. Roll the chicken wire into a cylinder with a 6 inch overlap, and fasten with 22 gauge wire (or extensions of the chicken wire itself) at the top and bottom with fasteners in between at about 3 or 4 inch intervals. The overlap of the roofing felt is to keep investment from leaking (bursting!) from the flask. 

6. VERY IMPORTANT – Use your pattern to check for proper fit inside the wire cylinder. There should be a minimum gap of 1 to 1 ½ inches between the sides of the pattern and the cylinder sides. The cylinder should be as high as the gated pattern standing on the block of investment you cast earlier. This flask illustrates how the gated piece should fit.
 

Note that the styrofoam cup is capped to keep it from filling with investment. 

7. If the pattern fits properly, roll the roofing felt around the chicken wire cylinder. (Make sure that the bottom surface of the flask is even so that it will seal to the floor properly.)  he flask is held together by temporary duct tape patches and then secured  with circumferential bands of duct tape. The bands should overlap at their ends by 4 or 5 inches. The bands should not be more than 8" or so apart (vertically) to maintain the integrity of the flask against the hydrostatic pressure of the liquid investment.  Leave an approximate 2" vertical gap between the lowest ring and the bottom of the flask. This gives the plaster that seals the flask to the floor something to bond to.

8. Cut a circle of roofing felt that will fit inside the cylinder.  (SEE ABOVE) it will be used as a floor for the investment flask. Its purpose is to keep the flask from bonding to the room's floor.

9. Seal the flask (that’s what you have just made) to the floor with plaster. A concrete floor is best.  A floor that is tiled or waxed won't do at all.  (Make sure the floor you are sealing to is clean and free of dust.) the plaster seal should come up the side of the flask about 2 inches, and extent out from the side about 2 ½ inches.

10. VERY IMPORTANT – wait until the plaster seal is COMPLETELY SET before pouring investment.

11. TO PREPARE THE WAX FOR INVESTING, Wash (brush) the pattern with alcohol to remove surface grease as an aid to making the investment adhere better.

12.   Preparing to set -up the holding buckets. 


Prepare however many holding buckets of dry investment you think you’ll need. Follow a set pattern in putting materials in the buckets. That way, if a mistake is made, it will be obvious, and can be corrected. A good procedure is to put the luto in first, followed by the sand and then the plaster last.  Further, it's a good idea to reserve the plaster in a can on the top of the rest of the mix.  That way, the plaster can be recovered if too much mix is made. ​ 

13. Place the cast block of investment in the flask (broad end up to guarantee that the block will not fall from the investment), and set the bottom end of the gating system on it. Check to see that the pattern is properly centered in the flask – make any necessary adjustments. Block the open end of the pouring cup by covering it with duct tape or , if you got a cup from a restaurant, use the cap that came with it.  Unfortunately, the lower end of the sculpture can't be seen here

18. A team member will have to hold the pattern in place while the pouring takes place. If possible, this person should be seated for steadiness' sake, and opposite the side from which the pouring takes place.

14. MIXING INVESTMENT – One person using the power mixer, and pouring investment while a second brings dry investment to be mixed and makes up more dry investment if necessary.

15. Put water in the mixing bucket first, use the mixer to agitate the water, add the dry investment while continuing to power mix. It can be done by one person! (Note the mixer in the bucket in the photograph on the right.)

16. Continue until the mix is smooth (about 2 minutes) – don’t take too long, the mix thickens appreciably after about four to five minutes. After that it becomes too stiff to pour properly.

17. After the initial power mixing, check the investment by hand (take the power mixer out before you do this!). If the mix is thorough and free of lumps, proceed to the next step. If not, power mix some more.

19. Start investing the pattern by pouring the mix into the flask. IMPORTANT - The mix is heavy and can break the pattern apart or shift it out of position. Avoid pouring the mix directly over the pattern or pouring from only one point in the flask.

20. If you’ve mixed 40 or 50 pounds of investment, you may find it easier to pour by using a bowl to pour smaller amounts than a bucket full all at once. An alternate method is to have the person who is holding the pattern in place put their hand over the top of the pouring cup with their fingers spread apart – the mix is poured over the hand which breaks it into a several small rivulets, and spreads it around the pattern.

21. After each batch is poured, agitate the mix in the flask. This helps to break bubbles that might adhere to the surface of the pattern (bubbles cause lumps on the surface of the cast), and helps ensure that fine detail is properly encased. In this photograph, she is reaching into the investment with her left hand and paddling the investment.

22. Usually, after the third or fourth batch is poured, the earlier batches have set enough so that the pattern no longer has to be held in place. N.B. this doesn’t mean that it should not be protected from poured investment.

23. Continue adding investment in this manner until the flask is filled. That is, the investment is almost to the top of the pouring cup. The top of the cup, and the vent assembly should just clear the surface of the investment.

24. Once the investment has set, the sealing ring of plaster at the bottom is broken away using a hammer and cold chisel. The duct tape bands are cut at the overlap joint, and the roofing felt is stripped away.

25. Any wire projecting from the top of the investment is cut away, the foam pouring cup is removed, the vent hole is cleared, and a channel (trap) is cut between the pouring cup and the vent(s).  The purpose of the trap is to keep any spilled bronze from slopping over and blocking the vent.  Then, use an air blast or brush to remove any loose crumbs of investment.

26. Carve your initials on top of the investment so you can identify your work after it is cast.

27. Transport the investment to the burn-out kiln. Place the investment so it can be heated evenly from all sides.

READY FOR BURN-OUT AND CASTING.

bottom of page