优化处理红宝石中轻微玻璃态物质的清理实验

针对目前市场上出现的一些因优化处理而产生轻微玻璃残余物的天然红宝石,经适当浓度的氢氟酸(浓度23%)浸泡后,位于红宝石内裂隙和表面凹坑中的轻微玻璃态残余物被溶解,达到清理玻璃态残余物的目的,并利用电感耦合等离子体-原子发射光谱仪(ICP-AES)分析含玻璃材料的溶液中Si和Al的浓度分别为28.60μg/mL和2.795μg/mL,进而估算玻璃态残留物的损失量以判定热处理过程中非人为加入的玻璃态物质在红宝石中的充填程度。利用红外光谱仪对玻璃残留物清理前后的红宝石红外光谱进行对比研究得出:清理前,红外光谱显示在1 100~1 000 cm-1内有1个单峰宽谱带,谱峰为1 050 cm-1,是由νas(Si—O—Si)非对称伸缩振动引起的,表明残留物为非晶质体,750~600 cm-1之间位于744 cm-1的吸收峰为νs(Si—O—Si)对称伸缩振动引起;清理后,未检测到玻璃残余物特征的Si—O振动峰,仅具950~600 cm-1范围内的宽谱带,为刚玉Al—O基频振动谱带736、622 cm-1,体现晶质金属氧化物的特征,表明样品中玻璃态物质已被清除,实验后红宝石可被划归为经人工优化范畴。宝石显微镜下观察到清理实验后红宝石中原先被玻璃残余物所掩盖的显著内裂隙及表面凹坑。

The experiments on the clearing of the glass substances in slightly glass-filled rubies

Natural rubies often show central grayish blue cores in their untreated state,which are usually considered to be of a low quality.Therefore,most rubies are artificially heat-treated at high temperatures to improve the color.During the heating process,the flux accompanied by the process is cooled down and becomes amorphous residues that remain in the fractures or surface cavities of ruby unintentionally,and thus the clarity and transparency of the ruby,to some extent,are enhanced.Subsequently rubies that have experienced the heat treatment are often identified as those with traditional filling treatment,by which the original thoughts of merely conducting artificial enhancement are misunderstood and the values of the rubies are influenced.This paper intends to remove the amorphous residues in the ruby on the experimental basis so as to reassign it to the acceptable range of pure heat enhancement,and in this way the appropriate value of the ruby could be shown on the gem market.The amorphous residues existent in natural rubies due to heat enhancement and treatment are cleared by immersing the rubies in the hydrofluoric acid(HF) with the concentration of 23% in which the glass residues that remain in the fractures and pits of ruby are readily dissolved so as to attain the goal of clearing.ICP-AES analysis of the hydrofluoric acid solution with the amorphous residue solute mentioned above was used to indicate the concentration of Si and Al,namely 28.60 μg/mL and 2.795 μg/mL respectively,by which the weight of the removed residues was roughly calculated so that the filling degree of the amorphous residues that unintentionally added to the ruby could be determined.Fourier transform infrared spectra of ruby specimens were determined before and after the clearing process for comparison.The infrared spectra of ruby prior to the clearing process showed that,in the range of 1 100~1 000 cm-1,the ruby exhibited broad band positioned at 1 050 cm-1 due to the unsymmetrical stretching vibration of νas(Si—O—Si),which indicated that the residues were amorphous.A sharp band centered at 744 cm-1 in the 750~600 cm-1 region corresponded to symmetrical stretching vibration of νs(Si—O—Si),whereas none of the characteristic Si—O vibrations caused by amorphous residues was detected by the infrared spectroscopy after the acid treatment of the ruby,and only a broad band in the range of 950~600 cm-1 featured at 736 cm-1 and 622 cm-1 was shown,which was caused by the Al—O fundamental frequencies of corundum and thus displayed the characteristics of crystallized metal oxide,suggesting that the amorphous substances in ruby were removed thoroughly and ruby specimens eventually fell into the pure heat-treatment(enhancement) category rather than the glass filling treatment category.After the performance of clearing experiments on the ruby specimens,the fractures and pits on the surface of the rubies which had previously been covered by amorphous residues were clearly visible under the gemological microscope.