METAL PREPARATION

Waxing

A minimum wax thickness of 0.2 mm is recommended for proper porcelain support (fig.1, 2) For single units use direct sprues with reservoirs. (Fig. 3)

1. Waxing	2. 0.2mm thickness	3. Spruing

 

Investing

- A low heat, gypsum based investment is preferred, but a high heat, phosphate based investment may be used. Cover top of pattern with no more than 1/4" (6 mm) of investment.

Burnout

- For gypsum investments, use the manufacturer’s recommended burnout temperatures and technique. Phosphate invested units should be burned out at 1250-1450°F (677-788°C), using a two-stage burnout procedure. A rapid-fire technique can be used following manufacturer’s instructions.

Casting

- Melt with a gas/oxygen torch with a multi-orifice tip. For automatic machines the casting temperature is 2200°F (1200°C).

- Use no flux during casting.

- Add 50% new alloy to clean buttons.

Divesting

- Divest castings carefully. Do not tap buttons or strike the investment, you may distort the casting. Remove investment by lightly blasting with unrecycled white 50 micron aluminum oxide at less than 30 psi / 2 Bars. Traces of Investment may be removed using hydrofluoric acid or acid substitute in an ultrasonic cleaner for 5-10 minutes. Ultrasonic 5 minutes in distilled water (fig. 4).

Finishing

If acid was used, it is not necessary to grind the entire casting. Grind porcelain-bearing surfaces as needed with fine crosscut carbide burs used at slow speed, which will cut the metal without "pushing it" (fig. 5-7). If acid was not used, prepare entire casting surface with carbide burs (fig. 8)

4. Single as cast	5. Cut off sprue		6. Grind sprue as needed
7. Completed metal preparation		8. Entire crown preparation (if acid not used)

Degas

- Place units in a preheated furnace at 1100°F (600°C) and raise the temperature to 1800°F (980°C) in air, hold for 5 minutes. Do not remove oxide (fig. 9).

9. Metal conditioning

 

 

 

 

Opaque

- For powder opaque, fire a thin wash of opaque 10°F (6°C) higher than the normal. (Fig. 10) For paste opaque, dry 5 to 10 minutes on a heat source prior to furnace firing.

- Ensure second opaque firings reach maturity. (Fig. 11) Porcelain Application

- Apply and fire porcelain normally. (Fig. 12)

A light internal blasting at less than 30 psi / 2 bars before glazing will enhance the golden color. Aluminum oxide blasting results in a matte finish. Blasting with glass beads results in a shiney surface.

- The internal surface will remain a rich golden color after firing. (Fig. 13) Additional detailed instructions are included within the following "Bridge Technique". [View Bridge Technique]

10. Wash opaque	11. Final opaque	12. Completed crown	13. Internal surface