Method 1: The Density Cup (Pycnometer)
The industry standard for gravimetric testing. It involves weighing a perfectly calibrated volume of liquid to calculate its mass divided by volume.
Step-by-Step Procedure
- Weigh Empty: Place the clean, dry cup and its lid on a precision balance. Record this as your Empty Weight (m1).
- Temper (Optional): Ensure the liquid is near standard room temperature (20°C / 68°F) to avoid thermal expansion errors.
- Fill: Pour the glaze/slip into the open cup until it is slightly overflowing and domed at the top.
- Cap & Purge: Press the lid straight down firmly. Excess liquid and trapped air will squirt out of the center vent hole.
- Clean: Use a damp sponge to wipe away the overflowing liquid, followed by a dry cloth. Warning: Do not press down hard on the lid while wiping, as it will draw liquid back out of the hole, ruining the volume.
- Weigh Full: Place the full cup back on the scale. Record this as your Full Weight (m2).
Method 2: The Syringe
A highly accurate, low-cost alternative to a traditional Density Cup. A 100ml or 10ml feeding/medical syringe (without a needle) provides an exact volume measurement without the cost of stainless steel equipment.
Step-by-Step Procedure
- Prepare Syringe: Ensure the syringe is totally clean and the plunger moves smoothly. (Tip: For very thick slips, you may carefully widen the plastic nozzle with a craft knife).
- Weigh Empty: Place the empty syringe on the scale and record the Empty Weight (m1).
- Draw Material: Submerge the tip into your well-mixed bucket. Pull the plunger back slowly to exactly the 100ml (or 10ml) line.
- Purge Air: If you see air pockets, point the tip up, tap the sides so bubbles rise, push the air out, and draw up more glaze to hit the exact volume line perfectly.
- Clean Exterior: Thoroughly wipe the outside of the plastic barrel so no excess glaze is weighed.
- Weigh Full: Place on the scale and record the Full Weight (m2).
Data Analysis & Quality Control
Recording specific gravity is only half the battle. This tool provides visual graphs designed to help you actively manage your studio's standards.
Understanding Batch Trends (The Line Graph)
The Trends graph plots your glaze density over time chronologically. By filtering for a specific material (e.g., "Tenmoku"), you can monitor its stability.
- Upward Drift: Indicates water is evaporating from your bucket over time. The glaze is getting thicker.
- Downward Drift: Indicates too much water was added during a mix, or wet dipping tools are diluting the batch.
- Sudden Spikes: Usually indicates a weighing error, a settling issue (the heavy particles sank to the bottom before testing), or a badly mixed new batch.
Using the Comparison Tool
When you achieve a perfect glaze firing, log that batch as your "Golden Baseline". Next time you mix that same glaze, select the Golden Baseline card and your New Batch card, and click Compare. The graph will instantly tell you exactly how far off your new batch is in percentage terms, allowing you to correct it before a firing disaster occurs.
How to Fix Deviations
If your graph shows your batch is too thick (higher SG than your baseline), go to the Lab Tools > Glaze Dilution Fixer. Enter your current SG, your target baseline SG, and the weight of your bucket. The app will calculate exactly how many milliliters of water you need to add to bring the batch back to perfect specification.
True Specific Gravity (Temperature Correction)
In pure physics, Density is Mass / Volume. Specific Gravity is the ratio of your liquid's density to the density of pure water at that exact temperature.
Because water expands as it warms, 100ml of water at 20°C weighs slightly less than 100g. By entering your liquid's temperature into the app, it utilizes Thiesen's scientific polynomial formula to calculate the exact density of water at that temperature, giving you a highly precise "True SG" reading.