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Drying Factor - DFACNotesThis test is designed to produce performance data from the speed-drying of a 12 cm by 5 cm thick rolled clay disk which has a 6 cm metal disk placed on its center. Many factors related to the clays mineralogy, plasticity, pugged integrity, particle size distribution, soluble salts content, etc. can be interpreted from the way and the degree to which the sample cracks, and the way its surface changes color during drying and firing. Procedure1. Purpose 2. Scope 3. Definitions 4. Responsibilities 5. Procedure 5.1. Create a FORESIGHT Record (QC) 5.2. Take or Make the Sample (Pugmill Operator, Test Sample Mixer) 5.2.1. (Same as SHAB test 5.2.1 to 5.2.2) 5.2.2. Deliver the sample to QC. 5.3. Make the Disk (QC) 5.3.1. Take approximately 500 grams of the pugged material and knead it for 30 seconds. Roll the kneaded lump into a cylindrical mass about twice as long as its diameter. 5.3.2. Place the lump on a canvas board straddled by two round metal rods of 3/16" (4.7 mm diameter). Position the lump so that the center axis runs away from you and use a rolling pin to roll it to about 1/2 as thick. Peel it up and without flipping it over turn it 90 degrees and roll half as thick again. Repeat until the rolling pin runs on the metal rods. 5.3.3. Carefully lift the slab of clay from both ends to free it from the canvas board and turn it over. 5.3.4. Use a divider or compass to cut a 12 cm diameter disk. Turn it over again and place it on one end of a bar board (use the other end to hold the SHAB bars). 5.4. Mark the Disk 5.4.1. Using FORESIGHT determine the ID# for the run or mix begin tested. 5.4.2. Prepare the stamp by setting it to stamp the ID# and a specimen number of 1. 5.4.3. Press the stamp into the disk in two places (opposite each other across the centre point) to produce clear easily-readable letters. 5.4.4. If multiple disks are being made (e.g. to assess drying performance for various custom stiffnesses in the run), then assign successive specimen numbers to each, and stamp or write these on each sample. 5.5. Dry the Disk 5.5.1. Within a few minutes after rolling the disk place it in an air-circulating 90-100C drying chamber. Put a 60 mm metal disk (or can filled with sand or plaster) on the center of each disk, leaving an even ring of exposed clay all around. Leave the samples in the drier until they are completely dry. 5.5.2. Accumulate dried disks in preparation for evaluation. When ready bring them to the computer for the next step. 5.6. Evaluate and Mark the Dry Disk 5.6.1. In FORESIGHT look up the Recipe or Results database record corresponding to the disk so it is displayed on the screen. 5.6.2. Break the disk into two halves if it has not cracked in two already. 5.6.2.1. Break the most poorly formed half to create a quarter circle with a visible stamped number in tact if possible. If this cannot be done write the number on the quarter disk with a ceramic pencil or scratch it in clearly with a needle tool so it can be read after firing. 5.6.2.1.1. Use a pencil to write the clay type on the specimen so it can be iddentified and included in a firing appropriate to its firing range. 5.6.2.1.2. Assign a drying factor as follows and enter it into FORESIGHT using the Testdata Entry Dialog: (Note: The IMC Magic of Fire book has a chart which graphically shows each of the following) There are four major crack types: The drying factor has four digits which are: Digit 1 Crack type I.E. B624- means: Crack type B, 6 cracks, a little less than 2 mm wide main crack, 4 cracks coming in from outer edge, not counting main crack. If D-type cracks are hairline then designate it as a C-type. The other digits will still alert the evaluator that concentric cracks were present. 5.6.2.1.3. If the SOLU test is not being performed discard the specimen, otherwise: 5.6.2.1.3.1. Enter a value into the computer or onto a log sheet for the degree of discoloration of the dry disk. 5.6.2.1.3.2. Accumulate quarter-disks for firing and further evaluation of soluble salt discoloration of the fired surface as described in the SOLU procedure. 5.6.2.1.3.2.1. Accumulate these samples in the dry bar holding area. Maintain a stack for each temperature (e.g. low, medium, high). When enough have been accumulated fire them or else include them in routine firings as opportunity arises. Fire them lying flat with solubles side up. 5.6.2.2. If the SOLU test is not being performed discard the specimen, otherwise: 5.6.2.2.1. Mark the half-disk as described in the SOLU test procedure. 5.6.2.2.2. Accumulate half-disks for bisque firing, glazing and evaluation of possible interaction of soluble salts with the glaze. 5.7. Record Notes 5.7.1. Print a test results report for each mix tested, compare and evaluate data as appropriate and enter notes for records where appropriate. 5.7.2. Report to management or production if needed. 5.8. Equipment 5.8.1. Disk Making and Drying 5.8.1.1. The same tools are needed as for the SHAB test with the following exceptions 5.8.1.1.1. Bar width guage, metal marking template and talc powder are not needed. 5.8.1.1.2. The thickness gauge must be 3/16 inch (4.75 mm). 5.8.1.1.3. A compass or divider which is suitable for cutting the 12 cm disk from the soft rolled clay is also needed. 5.8.2. Evaluation of Dried Disks 5.8.2.1. Vernier calipers accurate to 0.1 mm. 5.8.2.2. Ceramic pencil for writing on dried specimens (preferably a dark color like black). 5.9. Safety 5.9.1. Do not breathe clay dust unnecessarily. 5.10. Workmanship 5.10.1. Clay Preparation 5.10.1.1. Same as for SHAB test. 5.10.2. Making Disks 5.10.2.1. It is important to roll the clay exactly the same way each time to get consistent and comparable results. 5.10.2.2. Use a dry canvas board and peel the clay up frequently during rolling to make sure it does not stick to the board, making the back side of the specimens excessively rough and stretching the clay, thereby affecting the integrity of the test. 5.10.2.3. If the stamp does not produce a clean imprint press a little harder. If the clay lacks enough plasticity to make a readable imprint then write carefully with a needle tool. 5.10.2.4. When cutting the circular disk pay attention that the divider or compass does not change setting. Also, before cutting a disk, verify that the compass or divider is set at 12 cm. 5.10.2.5. It is important that the disks suffer minimal edge cracks as a result of rolling and cutting as these will affect the final drying factor. 5.10.2.6. If you must write on a disk with a sharp pencil or needle tool do it so that it is clearly legible for later data entry. Write in small letters to minimize the chance that a crack will start at the written label. 5.10.3. Drying 5.10.3.1. Stamping the ID# on each disk twice is helpful because if a disk cracks across one the other will likely still be readable and its section can be used for possible SOLU evaluations. 5.10.3.2. When breaking one of the disk halves to make the quarter disk for further use in the SOLU test, make sure both exposed and non-exposed surface areas are preserved. 6. Reference Documents 7. Reason for Re-issue VariablesDFAC - Drying Factor (V)There are four major crack types: SOLD - Salts on Dry DFAC (V)The drying disk will develop soluble salts around the out exposed edge. Rate these as either Nil, VLight, Light, Medium, Heavy. SOLW - Salts on Wet DFAC (V)Treat the same as dry disk. Out Bound Links
In Bound Links
Pictures DFAC dried disk showing soluble salts and drying performance crack typical of a plastic pottery clay body.  Drying disks used for the DFAC test to measure the drying performance of a clay  Example of a lab drier with heating elements, fan and temperature indicator  Solubles salts as visible on various DFAC test specimens  Albany Slip DFAC dried disk showing the soluble salts and characteristic cracking pattern and cut edge of a low plasticity clay.  A DFAC drying test disk of a terra cotta pottery clay from St. Ignacio, Sinaloa, Mexico. The wideness of the main crack indicates high plasticity, edge cracks indicate tendency toward crack propagation.  |
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