I can’t remove bits of rubber stuck
stones after mold-making.

If pieces of Castaldo® jewelry molding rubber become stuck behind stones in a metal model, the following techniques can be used to remove them.

First, try to dislodge the rubber with tweezers, a pick or similar tool. If that does not work, immersing the piece in warm soapy water in an ultrasonic cleaner may help.

If the rubber still cannot be released, consider the following techniques, depending on the type of rubber involved and the heat resistance of any gemstones that may be present. These techniques are potentially dangerous and can produce hazardous fumes and smoke. Please note the warnings and cautions below.

1. Natural rubber products such as Castaldo White Label®, Gold Label®, No Shrink Pink® and Titanium Label™

Use a torch adjusted for a relatively cool flame of about 450° or 600° F ( 230° – 315° C) and heat the area until the rubber becomes a brown liquid. This liquid can be easily dissolved with common solvents such as mineral spirits, acetone, etc. Caution: Models with solder joints may require an even lower temperature flame or may not be suitable for this method.

Please note that the burning rubber will drip and that the drips will burn exposed skin. Be careful!

If the flame is kept on the rubber longer or if temperatures are increased to 800° or 900°F ( 425°- 500° C), the rubber will burn, leaving ordinary carbon deposits that can be cleaned off as any other dirt would be by any common cleaning method, such as ultrasonics, etc.

If a torch is not available a match, cigarette lighter or gas-stove flame will also work.

Yet another technique is to put the model in an oven at the temperatures mentioned above.




Previously we recommended the following solvents. They work well at dissolving natural rubber. But they are becoming increasingly difficult to find because of their hazardous nature:

Tri -choloro ethylene (commonly known as Tri-chlor)
Methyl Ethyl Ketone (commonly known as M.E.K.)

These compounds may still be available from chemical supply houses and, in some cases, auto body paint supply companies and good quality paint stores, but usually not hardware stores.

Paint thinner and gasoline will also work but may take several days; the solvents listed above are much quicker.

Place the model and the solvent in a closed glass container with a tight lid and allow it to soak. The rubber will slowly soften.




2. Castaldo LiquaCast® LiquaCast Long Life™ and other non-silicone RTVs:

LiquaCast® cannot be removed with any known solvent. The flame method is the only one that will work. Only low temperatures are needed, such as those generated by a match or cigarette lighter. Please note that the burning rubber will drip and that the drips will burn exposed skin. Be careful!

3. Castaldo vulcanizing & RTV silicones

Vulcanizing silicone rubbers such as our Super High Strength™, VLT®, Rapido®, Super Stretch™ and Econosil® and our RTV silicones LiquaFast ICE™ and Quick-Sil® cannot be dissolved. On the other hand, they are unlikely to stick because they are filled with silicone oil and are thus self-releasing. If needed, mechanical means such as ultrasonic cleaners with warm soap and water solutions will often work.

If nothing else works, you may be willing to try a hot torch flame. This will turn the silicone rubber into a powdery gray ash that can easily be cleaned by conventional means. But the heat required ( about 1,650º F / 900º C ) may damage some types of precious stones. We urge caution when using this method and specifically deny any responsibility whatever for damages that may result from using this method. It is your responsibility to know the heat-resistant characteristics of the stones you are working with and make a judgment on that basis.

Be careful with fire and fumes when burning rubber. Use adequate ventilation and think fire safety! Work outside if possible.

Your safety and the safety of the stones is, of course, the first consideration. Use your judgment.


Copyright © 1991-2016 F. E. Knight Inc. ALL RIGHTS RESERVED