Before sharing the results of my experiments, I thought it might be of interest to review the various processes by which I pulverized these rocks. Along the way, I’ll also offer a brief assessment of the tools I’ve used, as well as presenting some alternatives and avenues for future projects.
Preparing the rocks
Depending on the initial size of the rocks, you may need to split them up so that the pieces can be crushed more easily. Compared with my previous tests, this time I decided to continue with my experiments using rocks of considerable size instead of pebbles ; this decision was taken, firstly, to amass a large quantity of the same material and, secondly, to ensure a certain chemical homogeneity of the powders produced. The latter is important as it guarantees, to some degree, relatively similar results over time.
That said, how do we go about fragmenting our rocks ? Depending on the tenacity of the rock, some tools are more effective than others. While some rocks are surprisingly fragile and can be virtually crumbled by hand, others are more tenacious and require robust tools, such as a hammer. As I demonstrate in the first part of the video (Figure 1), it’s possible to break these rocks with a few hammer blows and sometimes with the help of cold chisels. In the event that a rock doesn’t succumb to this treatment – as was the case – you’ll need other tools. For example, in the second part of the video, I’m using a hammer drill (Figure 2 and 3). In all honesty, without this tool, I would have abandoned the project or, at the very least, I wouldn’t have carried out these experiments with so many samples.
The material preparation stage is probably one of the most demanding both in terms of time and physical effort. Finally, there are other tools available to speed up and facilitate the process. A jaw crusher, for example, can efficiently crush rocks into small pieces, enabling you to move onto the next stage more quickly. I’ll come back to this tool later.
Rotary Hammer Drill.
Three attachments used for splitting rocks.
From rock to dust
Now that the rocks have been reduced to a suitable size, it’s time to turn them into a fine powder. Initially, I did this part “by hand”, using a hammer. More precisely, I made a sort of mortar and pestle using iron pipes (Figure 4 and 5).
To make your own, you’ll need:
- An iron pipe with an internal diameter of 2″ (~5cm) and a length of 6″ (~15cm) ;
- An iron twist cap for said pipe;
- A second pipe half the diameter of the container (~1″ or ~2.5cm) and twice as long (~12″ or ~30cm) OR 2 shorter ones attached by a coupling/fitting ;
- Two pipe cap at each end of the long pipe.
On another note, this prototype could be improved in a number of ways. For example, it would be preferable, among other things, to enlarge the surface area of the container to accommodate a greater volume of rock, or to use a more resilient striking rod – and a hand-protecting clamp – to enable the rod to be struck harder and with greater confidence.
This method, though effective, is physically demanding and time-consuming. Undoubtedly, this depends on the tenacity of the rock, but above all on the quantity of powder you wish to produce. For example, using this tool, I was able to produce almost 1kg of fine powder in 60-75 minutes. However, having accumulated nearly 40kg of raw material for this experiment, I needed to find other means. This problem is what led me to the construction and, later, purchase of a rock crusher tool.
Rock Crusher
A quick search on the Web led me to this neat little device that make use of an angle grinder to pulverize rocks into a relatively fine powder quite quickly – I’m speaking here of something between a mesh size of 40 and 80 in 30-60 secondes, although a longer running time could produce a finer mesh size.
Initially, the price of this type of tool prompted me to build my own version. I won’t necessarily go into detail about the construction of my prototype as there are many tutorials on Youtube. Generally speaking, its layout isn’t very complex; what counts is having the right tools to build it. For example, you can find different variations of this machine on the Web. Some will require you to weld certain parts, while others won’t. In my case, the build took a while because the tools at my disposal, and obviously my skills, weren’t necessarily capable of producing parts with the required precision and/or finish. As a result, there are several aspects of my prototype that need to be improved. That said, although it was “acceptable” in terms of operation, its durability was not up to my expectations. For example, the main axle on mine is not as sturdy as the one I bought.
The first set of photographs (Figure 6) showcase the prototype I built while the second is the one I ended up purchasing (Figure 7).
Compared to my prototype using steel chain (extremely durable), this one uses stainless steel shackles (relatively less durable) – see figure 8 for the wear and tear. Although it was easy to change the shackles, I wish this model could have made use of more tenacious parts. Finally, another drawback of this machine is that the inlet tube is relatively small and, consequently, requires additional time and effort to break up the rock so that the pieces can slide into it.
The life cycle of a shackle.
Finally, acquiring this tool enabled me to speed up the process considerably. Indeed, as I mentioned earlier, the “hand” method enabled me to produce close to a kilogram of powder in 60-75 minutes, whereas this one enabled me to process close to 5 kilograms within a similar amount of time. Following pulverization, I passed the powder through a sieve with a mesh size of 40. My estimation is that around 85% of the powder sits between a mesh 40 and 60, the rest being smaller.
Health and Safety
It goes without saying that the various processes used to grind stones into a fine powder create both debris and, above all, dust. That’s why it’s important to be properly equipped (Figure 9).
For example, I strongly recommend wearing safety goggles in the (highly probable, I’d say) event of some debris being launched towards your eyes. I can attest that this happened to me several times during the process. More importantly, I recommend wearing a half-face dust mask using P100 cartridges (or better), as the dust created can be harmful to your health.
Finally, because of the noise produced by the crusher, you might want to consider hearing protection. As for wearing gloves, this may vary according to the minerals present in the rocks and your preference.
Variations, Alternatives, and Future Projects
Earlier, I discussed the different processes used in my experiments. That said, there is a wide range of tools available to us for producing glazes from raw material. In this section, I’d like to share a few alternatives. At the outset, I mentioned the use of a kind of mortar and pestle made from iron pipe – of course, you can also use a normal stone/steel mortar and pestle (Figure 10). On the other hand, you can find an alternative which, I believe, may be easier to use because it doesn’t require constant hammering (Figure 11). Also, I was able to find, on the Web, a similar tool using a pneumatic hammer (video example 1 ; video example 2 ; Figure 12). However, the effectiveness of this tool (and its variations) is highly dependent, on the one hand, on the tenacity of the rock and, on the other, on your physical capabilities. Consequently, I would only use and recommend this method if your intention is to produce small quantities (<2 kilogram).
Next, a tool I’d love to add to my arsenal is a jaw crusher. For example, the Crazy Crusher (Figure 13; video demonstration here) could speed up the process significantly. More specifically, its use would be relevant for fragmenting stone so that it can more easily be crushed in the machine crusher shown earlier, especially as this would reduce the rate of degradation of stainless steel shackles.
At last, another machine I’d like to acquire is a ball mill (Figure 14) – It’s also worth knowing that you can turn your pottery wheel into a ball mill with certain attachments (Figure 15; Figure 16)! Firstly, its mechanism enables relatively effortless grinding, although it needs to be given ample time to obtain the anticipated results (between 4 and 24 hours); secondly, the ball mill can produce an extremely fine, even industrial-grade ceramic powder (mesh size 250-325). This latter point is important, as materials act differently depending on their granularity. For example, silica (quartz) seems to melt better at a finer mesh size than a coarser one; therefore, we can encourage a smoother, more uniform fusion/melting of our glazes by paying attention to its mesh size. Finally, some tools are more useful than others, depending on the toughness of the rock and desired granular size. In fact, some rocks benefit from calcination, a process that “breaks” certain bonds in the stone by heating them between 550-1150C, making it easier to crush, to the point where some can be virtually crumbled by hand. However, for rocks whose composition includes some form of clay, this process could have the opposite effect.
All in all, there is a wide range of tools available to us for transforming rocks into fine powder for ceramic glazes. I hope that this publication will have shed some light on the various procedures that can be used in this process.
I’d love to read/hear your comments on this ! If you’re already producing glazes from rock: how do you go about it ? If you’d like to start your adventure in this type of approach: what would you like me to discuss further ? What else would you like me to write about ?
Thank you for reading 🙂
N
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