RCS (Respirable Crystalline Silica) also known as alpha-quartz, cristobalite or ‘free silica’ is present in clays, slips, glazes, colourants and other ceramic materials.
RCS is hazardous by inhalation as the ‘respirable’ dust, which is very fine and invisible under normal lighting, can get deep into the lungs.
High dust levels result from carrying, opening and tipping or scooping glaze and colour powders.
Contaminated work clothing may also be a source of dust exposure, even after the task has been completed.
Inhaling RCS can lead to:
Silicosis, which is a serious and irreversible lung disease that can cause permanent disablement and early death. There is an increased risk of lung cancer in workers who have silicosis.
Chronic obstructive pulmonary disease (COPD), which is a group of lung diseases, including bronchitis and emphysema, that results in severe breathlessness, prolonged coughing, chronic disability and can lead to death.
RCS dust is also abrasive and drying when in contact with skin, and can lead to contact dermatitis.
Wear appropriate RPE (respiratory protective equipment) P3 grade dust mask
Wear appropriate PPE (personal protective equipment) goggles, gloves, aprons
Personal decontamination with water, soap, towel, pre and after work skin cream
Contaminated work clothing to be washed frequently
Keep containers of powder closed when not in use, and during transfer between storage and mixing stations.
Reduce direct contact with raw materials, especially colouring oxides and colourants through the use of mixing and measuring tools
When mixing materials use a ventilated enclosure (spray booth and overhead extractor) with local exhaust ventilation (LEV).
Acquire and familiarise yourself with material safety data sheets before working with a raw material of your choice. Manufacturers by law have to provide these data sheets either on their website or upon request.
A step by step guide to working with ceramic materials
You must wear RPE/PPE and follow health and safety protocol. Put on a dust mask (P3 grade) and switch on studio extractor and spray booth. While carrying out the following tasks you must work within the spray booth with waterfall and extractor switched on. When measuring out very small quantities, you can work with only the overhead studio extractor switched on.
Locate and gather each material in your recipe and make sure you have enough of each ingredient.
You must handle containers with extreme care. Never grab them by the lid, lift them holding the bottom. Screw top containers must be closed tightly while snap lock containers must have their lids pressed down all the way around until they are completely sealed.
Clean your digital scale and make sure it is properly balanced before you begin
Place the measuring container for weighing your materials on the scale. With no materials in the container, the indicated weight should be set to grams at zero point. If not, adjust the tare compensation of the scale so that it reads zero.
Prepare glaze container: lid and container must be secure and air tight, and container must be labelled clearly. No food containers to be used unless their labels have been removed completely. (You are not allowed to use glass containers as they are often heavy and can cut you if broken.)
Fill glaze container with small amount of water (lukewarm water helps with blending raw materials)
Write your glaze recipe on a fresh piece of paper with required quantities for each component. Tick off each component when added to the mixture.
Weigh out each successive material and place it in the mixing container gently so to minimise airborne particles.
Add enough water to make a mixture the thickness of double cream. If too much water is added you may have to wait 24 hours before the materials settle and the excess water separates on top.
If mixing a small quantity (up to 2kg) you can use an electric blender. Larger quantities should be mixed with a peddle drill bit or an industrial glaze mixer. Safety goggles must be worn while mixing materials. Once the glaze is properly mixed with water, you may remove your mask and goggles.
Place a sieve supported by two sticks on top of another mixing container.
Pass the glaze mixture through the sieve twice (you can use a stiff brush to force the glaze through the sieve). This homogenizes the mixture and gets rid of any lumps. (Choosing the mesh size of your sieve can have an impact on the finished glaze. The lower the number, the courser the glaze. In certain cases where a rough and uncontrolled effect is desired the maker may decide not to sieve at all.)
Generally speaking our studio glazes are sieved through an “80” sieve as this will yield good results.
(If you have made up a large amount of glaze (more than 2000g) it greatly speeds up the process if the mixture is passed through a course sieve (60 mesh) before using a fine sieve (200 mesh).)
Some materials like Copper Carbonate and Bone Ash have to be ground down in a pestle and mortar before they are forced through the sieve. These materials clump together and it is easy to see that they need to be ground. (In some cases you may decide to skip sieving your colouring oxides or stains as some of them may not go through a fine sieve. In this case you would add the oxides or stains straight to the already processed glaze mixture)
Move the sieve over to the original mixing container and pour the glaze through the sieve once more. This time the mixture will pass through much easier.
Using a graduated cylinder measure out 100ml of glaze. Make sure you do not include the weight of the plastic container. Establish the specific gravity of the mixture. Studio glaze recipes will indicate what to aim for.
For example. If a glaze recipe calls for a specific gravity of 151 and your mix is 156, you will need to add more water so that you reduce/dilute how much raw material you have in 100ml of water. If your mixture reads 142 then you will have to wait a while until the mixture settles so that you can syphon off some of the excess water. This may take as long as a couple of days.. If a mixture is too thin, place a label on the container so it is not used until the specific gravity has been resolved.
Mark your container and store safely. Make sure that your notes and containers correspond otherwise you will not be able to make sense of your research.. A dedicated notebook and a personal record keeping system that you understand is very important.