There are many kinds of gypsum powder, such as medical gypsum powder, edible gypsum powder, gypsum powder for cement, etc. the conventional detection method of general gypsum powder is to judge from the color and hand feeling: generally, gypsum powder with high whiteness has fine fineness, good quality and high price; Gypsum powder for general handicrafts requires high whiteness and hardness, while gypsum powder with gray black and black impurities is of poor quality. Twist the gypsum powder with the thumb and index finger of the hand. The gypsum powder with rough hand feel has rough fineness, poor quality and low price; The gypsum powder with fine hand feel has fine fineness, good quality and high price.

具體的石膏粉的細度如何檢測呢？宇恒建材總結了以下幾個步驟：

How to detect the fineness of specific gypsum powder? Yuheng building materials summarizes the following steps:

①取待測石膏粉樣品約60g置于電熱鼓風干燥箱中，在40±4℃下烘干至恒重，將烘干后的試樣放入干燥器中冷卻備用（當有效干燥時間相隔1h的兩次稱量之差不超過±0.2g時，即為恒重）。

① Take about 60g of gypsum powder sample to be tested, put it into the electric blast drying oven, dry it to constant weight at 40 ± 4 ℃, and put the dried sample into the dryer for cooling and standby (it is constant weight when the difference between two weighings with an effective drying time interval of 1H does not exceed ± 0.2g).

②稱取50±0.1g試樣石膏粉置于篩內，用手指輕輕壓碎團塊，蓋上篩蓋，套上篩盤，按以下方法進行操作：一只手拿住篩，略為傾斜，搖動篩子，使其撞擊另一只手，搖動的速度為每分鐘125次，篩擺的幅度約為20cm。每搖動25次應使篩子向一定方向旋轉90度角，使試樣均勻散開（也可采用機械振動法過篩），直到篩到1分鐘內通過篩子的試樣少于0.1g時為止，稱取篩上物質量（篩余），數值為0.01g。

② Weigh 50 ± 0.1g of sample gypsum powder and put it in the sieve, crush the mass gently with your fingers, cover the sieve cover, put on the sieve plate, and operate according to the following methods: hold the sieve with one hand, tilt it slightly, shake the sieve to make it hit the other hand, the shaking speed is 125 times per minute, and the swing range of the sieve is about 20cm. Rotate the sieve 90 degrees in a certain direction every 25 times to make the sample disperse evenly (mechanical vibration method can also be used for sieving), until the sample passing through the sieve within 1 minute is less than 0.1g, weigh the mass on the sieve (sieve residue), and the value is 0.01g.

③按以下公式計算篩余量:C=B/A×100%

③ Calculate the screen allowance according to the following formula: C = B / A × 100%

式中：C為篩余量，%；

Where: C is sieve residue,%;

B為篩上物的質量，單位為克（g）；

B is the mass of the material on the sieve, in grams (g);

A為試樣石膏粉的原始質量，單位為克（g）；

A is the original mass of gypsum powder of the sample, in grams (g);

如果某種石膏粉之前不知道其細度（目數），可采用套篩（比如80目、100目、120目、140目、160目、180目等），機械振動法過篩，檢測各篩目篩余量，以確定該石膏粉的細度（目數）到底是多少，也可以反映出該石膏粉的細度（顆粒）分布。

If the fineness (mesh) of a gypsum powder is not known before, a set of screens (such as 80 mesh, 100 mesh, 120 mesh, 140 mesh, 160 mesh, 180 mesh, etc.) can be used for screening by mechanical vibration method to detect the screen residue of each mesh, so as to determine the fineness (mesh) of the gypsum powder and reflect the fineness (particle) distribution of the gypsum powder.