Testing Your Kiln's Temperature

by Janet Alexander

 Now that most kilns have a computerized controller it’s become easier to control the kiln’s temperature. But, is the controller’s readout accurate? With so many varieties of bronze, copper, and silver metal clays, it has become important to know if your kiln’s temperature reading is correct. Otherwise, you may have problems with the clay not sintering correctly or getting too hot and melting. Additionally, the kiln should be tested for hot spots and cooler spots. Every kiln is different.





Testing can be done by using a pyrometer (which is how I used to adjust my kiln’s temperature before there were controllers) or by using kiln pyrometric cones. The pyrometric cones are supposed to bend when heated to a specific temperature for a certain amount of time. That means that pyrometric cones give a temperature equivalent; they are not simple temperature-measuring devices. According to a pyrometric cone manufacturer, cones have over 20 variables that can affect the cone’s bending, including the cone's composition, particle size of raw materials, type of forming process, moisture during forming, density of the cone, geometry of the cone, setting height, and angle and the heating rate. Atmosphere also affects bending behavior. Wow, that’s a lot of variables!  So, let’s look at testing with a pyrometer or a kiln test kit.

I used the kiln test kit sold by the PMC Connection. According to experts, the average kiln controller is accurate to ±10°F (±5.5°C) so keep this in mind while testing. Additionally, run the test several times but move the thermocouple to different areas of your kiln. Place it towards the back, near the front, off to each side, and etc. Test at different temperatures. I conducted tests at 1110˚F, 1200˚F, 1290˚F, 1470˚F, 1560˚F, and 1650˚F. I found that both readouts were within a few degrees of each other until the temperature got up to 1650˚F. Then they were off by 10˚F! So, I added another thermocouple from my casting kiln.  All three read different degrees but were within the accuracy range.

Now I know why my PMC3 clay had a crystalline look to it when I fired it at 1650˚F; it was getting too hot! So, now I lower the temperature of my kiln by a few degrees when setting it at 1650˚F.

The Test Kit Includes:

• Sensor  reader (tester)
• 9V Battery 
• K-type thermocouple TP-02A  
• K-type thermocouple TP-03 
• Case 

Use the TP-02A thermocouple (larger one) for testing your kiln. It has a temperature measuring range of (-58˚F to 1650˚F).



The Steps

1.  Install the 9 V battery into the unit’s back.

2.  Insert the plug into the bottom of the sensor reader making sure the plug’s polarity matches with the sensor’s polarity. 

3.  Insert the thermocouple into the kiln.

Caution: Don’t insert it past larger ceramic end or the wires will burn!

4.  Place the thermocouple near the kiln’s thermocouple for the first run of testing.

5.  Turn on the kiln and set it to hold at the test temperature for at least 15 minutes.

The sensor reader can read in Fahrenheit (F) or Centigrade (C). Turn it on by sliding the button from the center (off position) to the F (if measuring in Fahrenheit).

6.  The sensor displays its reading. Allow it a minute to stabilize to the temperature. Test at various temperatures. I found that my kiln was accurate until it reached over 1350 (F).

7.  When finished testing, turn off kiln and sensor reader and allow the thermocouple to cool before touching it.

Vibratory Tumblers

How is the Tumble-Vibe different from a rotary tumbler?

The basic difference between a vibratory and a rotary tumbler is the way the unit is driven.  A rotary tumbler consists of a barrel that sits on rollers causing the barrel to spin. Polishing media and the objects to be polished (jewelry pieces) are placed inside the barrel. As the barrel spins, the contents fall and slide over each other causing abrasion or polishing to the jewelry pieces located in the top 1-inch of the sliding media.  Jewelry pieces not located in the top inch are not polished. Some items can become dented due to the polishing media falling on the jewelry pieces.  It can take hours, days or weeks to bring a piece of jewelry up to a high shine using this type of unit. The lid on the barrel can leak or come off during the process.
 
A vibrating tumbler includes a bowl that sits on an out-of- balanced motor. As the motor moves, it causes the bowl to vibrate in all directions. The polishing media and jewelry pieces are placed inside the bowl. The bowl’s vibration causes the objects in the bowl to rotate around the bowl in two directions rubbing and polishing the jewelry 100% of the time. The items are polished much faster than a rotary tumbler and there is no chance of leaks, spillage, or denting of pieces. The items can be easily retrieved by opening the lid and fishing through the polishing media.

 A variety of different media, from cutting, to polishing, can be used in the vibratory tumbler including ceramic and plastic abrasives, walnut shells, and steel shot, making the vibrating tumbler more versatile than a rotary tumbler. The ceramic and plastic abrasives are sold in different grits. Polish is embedded in the walnut shell with the same polish jewelers use on buffing wheels. Steel shot, due to its hardness, is used as a burnisher. As it moves across the jewelry it rubs and burnishes the outer layer of the metal. 


General Instructions for the Raytech TV-5 Model

• The working capacity* of the Tumble-Vibe 5 is approximately .05 cu. ft. (three pints) or 4 pounds. The capacity includes the media, water and the work pieces.
• If the tumbler will be used for polishing as well as for cutting, always reserve one bowl strictly for the polishing media so it can remain free from embedded cutting grit.
• Successful finishing of most jewelry requires preparing the jewelry. Parts must be filed, sanded, or ground smooth over rough areas. Attempting to finish jewelry parts without adequate preparatory finishing can result in very long finishing cycles and loss of detail in the jewelry pieces.
• All plastic media or ceramic media should be broken-in before using. Media that is not broken-in may cause scratches. (See separate section, below, for breaking-in plastic media.)
• Keep a 70% media to 30% jewelry ratio. Too many items tumbling at one time can produce a poor finish.
• Always use cutting/burnishing soap with the media as required.
• If using steel shot, fill the bowl with water so that it just covers the top of the shot. Never completely fill the bowl with water. Too much water or soap hampers the media’s action. After tumbling, remove and dry shot.
• If using plastic or ceramic media, add 1 ½ oz. of water and a ½ teaspoon of polishing compound. Note: if the machine does not roll the media well at the start of a cycle, there is too much water or soap.
• Change water if it becomes gray or loses its suds. Rinse the bowl and clean the media.
• If the media tumbles too long without replacing the water, the jewelry pieces will absorb the gray sludge which is very hard to remove. The manufacturer recommends changing the water every three hours.
• When using ceramic media, don’t allow the bowl to run dry. This will cause premature wear on the bowl.
• Walnut or other shell media do not require water. Fill the bowl ¼” below the center cone and jewelry items.
• On average, dry polishing media is good for polishing up to 200 hours of use. When not in use, store in an air-tight container. See manufacturer’s instructions.
• Do not use media filled with silicon carbide or alumina powders as this will impinge and impregnated the metal surface and retard polishing.

NOTE: THE TV-5 UNIT CAN BE USED WITH UP TO 4 LBS. OF STEEL SHOT/CERAMIC MEDIA AND JEWELRY.

Breaking-in Plastic/Ceramic Media
1.   Place media into tumbler bowl.
2.   Add water and polishing compound /soap.
3.   Tumble without jewelry for one to two hours.
4.   Rinse media and bowl. Rinsing the media in a colander works well.

No More Maring Your Metal While Holding it in a Vise

All jewelry tools are made smooth without teeth so that they don't mar the finish of your work. But, sometimes it's helpful to have a vise with gripping teeth to hold various objects.




If you buy a bench vise at a discount store, it's not necessarily made for working with non-precious metals while making jewelry. You may need to smooth it in order to hold a piece of soft silver without marring it. So what do you do?









To solve this problem and have the best of both worlds by covering the jaws of your vise grip with copper sleeves.

1. Anneal the copper to make it malleable.
2. Cut two pieces of copper with the following dimensions: Width (equal to the width of the jaw) x Length (twice the height of the jaw).
3. Place one copper piece into the vise closing it tightly.
4. Using a rawhide mallet, hammer the copper down over the top of the vise.
5. Repeat the process with the other copper piece. 

Viola! You have a nice smooth surface inside the vise. When you need to use the vise with teeth, remove the copper.