Complete 2014 Catalog

TUMBLING INFORMATION

69

USINGTUMBLINGABRASIVES The main principle in polishing stone is to start with a coarse abrasive for grinding, and work through a series of increasingly finer abrasives to the final polish. The process is basically simple, but there are variations in gemstone properties, types of abrasives, many recom- mended grit (abrasive) sequences, and results produced by the different types of tumblers. All these variations and choices can be confusing, especially to a beginner, so it should be remembered that tumbling is basically simple, not an “exact science”, and can be great fun once the basics are mastered. The first choice to be made is the type of tumbler to be used, Rotary or Vibratory. A brief description of the two types is given on page 59. Further descriptions can be found on the pages in this catalog listing the tumblers themselves. Both rotary and vibratory tumblers use the standard silicon carbide grits with water in the mix as well as a filler of some type. However, Vibra-Dry mixes can be used in vibratory tumblers for the polishing steps, and produce higher polishes on almost all stones and metals. (See page 71.) Vibra-Dry mixes do not use water, and can be re-used multiple times. The beginner should be aware that some stones will not polish in either type of tumbler nor with any grit sequence. In order not to waste your time and money, be selective. See section on “Selecting Stones”. Over the years, individuals have developed procedures and grit sequences that give them good results. As a result, you will find that advice, books and manufac- turer’s instructions vary in their recommendations. All follow the basic principle of tumbling, but reading “Use 80 grit to start” in one source and “Use 60/90 to start” in another is confusing. Both work, and there is actu- ally little difference between those grit sizes. In fact, most grit sizes that are used actually cover a range in particle size. Finer grits and polishes are more closely graded so that particle size is more uniform and so are the results. Finer grits and polishes are more expensive. Fillers are recommended for use in both types of tumblers and in each step in almost all grit sequences. Fillers soften the action, fill space between stones, and carry the grit to the stone’s surface more efficiently. Fillers generally can be reused if thoroughly cleaned between grit sequences. We recommend the ceramic bits for both stones and metals as they seem to do the best job and will last longer.

ROCK FOR TUMBLING

Package contains assorted gemstonematerials of suit- able size and hardness for tumbling. Mixed varieties, sorry no choice. Stone size varies, but averages 1" in diameter. Can be broken into smaller pieces if desired.

Approximately 2 lbs. per package. 403-TR-10............Shp. Wt. 2 1 ⁄ 2

lbs.................12.75

SELECTING STONES

It is important that you select stones that will polish in order to be successful at tumble polishing. The looks of rocks can be deceiving, but in general, those with a hard surface and sometimes shiny look to them, are likely to polish. Stones with hardness of around 5 to 7 1 ⁄ 2 on the Moh Scale of Hardness are best. This includes the agates and jaspers which are the easiest to polish. Softer and harder stones, and certain stones such as Apache Tears and jade are special chal- lenges, and require special procedures.

MOH SCALE OF HARDNESS

1. Talc

6. Orthoclase

2. Gypsum 3. Calcite 4. Fluorite 5. Apatite

7. Quartz 8. Topaz

9. Corundum

10. Diamond S CRATCH TEST FOR HARDNESS

Use the simple field test below to identify the relative hardness of a stone. Stones in the range of 6.5 to 7.5 will usually polish well. Fingernails scratch 2 to 2.5 Pennies scratch 3 Knife blades scratch 5.5 Window glass scratches 5.5 Steel files scratch 6.5 Garnet scratches 7 to 7.5 Carborundum scratches 9.5