Method for changing grey green jadeite into red jadeite by oxidizing and heating, product and application thereof

Abstract

The invention relates to the technical field of emerald color changing, and particularly discloses a method for changing gray green emerald into red emerald through oxidation and heating and application of the method. According to the method, potassium permanganate is selected as an oxidizing agent, the grey green jadeite can be efficiently and uniformly changed into red jadeite by controlling the heating temperature and the heating time, and the color-changed product has the characteristics of high chromaticity and good stability and can be widely applied to the fields of jewelry, artwork and collections. Compared with red jadeite obtained through a traditional heating mode and ferrous carbonate and ferrous oxide powder covering heating, the color change is more thorough through potassium permanganate auxiliary heating, the added potassium permanganate powder is not directly attached to the jadeite raw materials, no chemical substance is additionally added to the jadeite raw materials, and the due characteristics of natural jadeite are reserved. The method provided by the invention is simple and low in cost, the color of the obtained red FeiCui is close to that of natural red FeiCui, and the color is natural and durable.

Description

Technical Field

[0001] The present invention belongs to the technical field of jadeite color improvement, and particularly relates to a method for oxidizing and heating grey-green jadeite to change its color to red jadeite, as well as its products and applications. Background Art

[0002] Grey-green jadeite often has a low market value due to its incorrect color, being grey and dull. Moreover, grey-green or brown-yellow jadeite formed by secondary genesis will gradually change its original color, namely the so-called "variant" phenomenon, during the wearing process due to long-term contact with air. The vast majority of red jadeite on the market precisely utilizes such a principle. By means of artificial intervention, it is kept at a constant temperature for a period of time at a relatively high temperature to accelerate the color transformation, thereby improving the quality value of the original low-color jadeite and meeting the market demand for red jadeite.

[0003] Heat treatment technology is widely applied in the research field of gemstone color improvement. The mechanism of its action on jadeite color improvement is mainly that high temperature converts divalent iron inside it into trivalent iron, and at the same time, dehydration occurs, making limonite with a yellowish tone transform into hematite with a reddish tone. Due to the scarce output of natural red jadeite, heat-treated red jadeite occupies a large share in the jade market. However, the problem faced by heat-treated red jadeite is to minimize the loss of moisture while improving the color of red jadeite. Chinese Patent CN202210942828.3 discloses a method for changing the color of yellow jadeite to red jadeite. On the basis of traditional heat treatment, an additional colorant ferrous carbonate or ferrous oxide is covered on the surface of the jadeite, and the divalent iron ions are transformed into trivalent iron ions by the buried burning method to change the color of yellow jadeite to red jadeite. This method has defects in chemical stability and may produce white precipitates due to out-of-control redox reactions or the problem of excessive migratory iron.

[0004] Therefore, how to provide a more stable and environmentally friendly method to change the color of grey-green jadeite to red jadeite has become an important research direction. Summary of the Invention

[0005] The purpose of the present invention is to provide, in view of the deficiencies in the prior art, a method for oxidizing and heating grey-green jadeite to change its color to red jadeite and its application. By controlling the dosage of potassium permanganate, heating temperature, and heating time, this method can efficiently and uniformly change the color of grey-green jadeite to red jadeite, and the product after color change has the characteristics of high chroma and good stability, and can be widely applied in the fields of jewelry, artworks, and collectibles.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions: The first aspect of the present invention is to provide a method for oxidizing and heating grey-green jadeite to change its color to red jadeite, comprising the following steps: S1. Polish and buff the greyish-green jadeite sample to be processed. S2. Heat the greyish-green jadeite sample obtained in step S1 and potassium permanganate for a preset time, and cool to obtain red jadeite.

[0007] Further, in step S1, the purity of the potassium permanganate is not less than 88%.

[0008] Further, in step S2, the mass ratio of the greyish-green jadeite sample to potassium permanganate is 1:(1.15 - 1.81).

[0009] Further, the heating process is as follows: at a heating rate of 2 - 5 °C / min, heat from room temperature to 400 °C - 500 °C, and keep warm for 4 - 8 h.

[0010] Further, the heating device is a muffle furnace or a tube furnace.

[0011] Further, the greyish-green jadeite sample is natural jadeite.

[0012] Further, the CIE-Lab data of the red jadeite shows that the L value is greater than that of the natural red jadeite sample.

[0013] Further, the refractive index of the red jadeite is between 1.66 and 1.67.

[0014] Further, the first derivative ultraviolet-visible diffuse reflectance spectroscopy data of the red jadeite shows an absorption peak at 540 - 580 nm.

[0015] The second aspect of the present invention is to provide the application of the above method in the preparation of jewelry, artworks or collectibles.

[0016] The red jadeite prepared by using the method provided by the present invention can be used to make rings, necklaces, bracelets or earrings; it can also be used for carving artworks or displayed as collectibles.

[0017] Compared with the prior art, the beneficial effects brought by the technical solution provided by the present invention are as follows: (1) Compared with the red jadeite obtained by traditional heating methods and heating with ferrous carbonate and ferrous oxide powders, the color transformation of the red jadeite assisted by potassium permanganate is more complete. The CIE-Lab data shows that the changes in red and yellow tones are higher than those of other heating groups, and are closer to the parameters of natural red jadeite. The concentration of hematite indicated in the first derivative ultraviolet-visible diffuse reflectance spectrum is higher.

[0018] (2) The potassium permanganate powder added in the present invention does not directly adhere to the jadeite raw material, and does not add any chemical substances to the jadeite raw material additionally, retaining the inherent characteristics of natural jadeite.

[0019] (3) The method provided by the present invention is simple and low-cost. The obtained red jadeite has a color close to that of natural red jadeite, and the color is natural and durable. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Pictures of the jadeite in Example 1 before and after heat treatment assisted by potassium permanganate; Figure 2 Pictures of the jadeite in Example 2 before and after heat treatment assisted by potassium permanganate; Figure 3 Pictures of the jadeite in Example 3 before and after heat treatment assisted by potassium permanganate; Figure 4 Pictures of the jadeite in Example 4 before and after heat treatment assisted by potassium permanganate; Figure 5 Pictures of the jadeite in Example 5 before and after heat treatment assisted by potassium permanganate; Figure 6 Pictures of the jadeite in Comparative Example 1 before and after conventional heat treatment; Figure 7 Pictures of the jadeite in Comparative Example 2 before and after conventional heat treatment; Figure 8 Pictures of the jadeite in Comparative Example 3 before and after conventional heat treatment; Figure 9 Pictures of the jadeite in Comparative Example 4 before and after heat treatment with ferrous carbonate coating; Figure 10 Pictures of the jadeite in Comparative Example 5 before and after heat treatment with ferrous oxide coating; Figure 11 Pictures of the jadeite in Comparative Example 6 before and after conventional heat treatment; Figure 12 Pictures of the jadeite in Comparative Example 7 before and after heat treatment with ferrous carbonate coating; Figure 13 Pictures of the jadeite in Comparative Example 8 before and after heat treatment with ferrous oxide coating; Figure 14 Appearance characteristic diagram of relatively typical natural red jadeite; Figure 15 UV-Vis diffuse reflectance spectra of each example and comparative example after heating; Figure 16 First derivative spectra of UV-Vis diffuse reflectance of each example and comparative example before and after heating. DETAILED DESCRIPTION OF THE INVENTION To make the objectives, technical solutions, and advantages of the present invention clearer, the following further describes in detail the specific embodiments of the present invention in conjunction with specific examples and drawings. For those not specifying the specific test methods, instrument equipment, or conditions in the examples, they shall all be carried out according to the techniques or conditions described in the literature in this field or according to the product instructions. For the reagents or instruments not indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0021] A method for oxidizing and heating a greyish-green jadeite to change its color to a red jadeite provided by the present invention is as follows: (1) Grind, polish, and clean the small pieces of jadeite to be processed. Use a spectrometer to test and obtain the CIE-Lab data and ultraviolet-visible diffuse reflection curve before heating.

[0022] (2) Place the greyish-green jadeite sample to be processed in a corundum crucible, and take a certain amount of potassium permanganate powder and place it in a clean crucible. Put the two crucibles together in the furnace chamber of a muffle furnace and heat according to the set condition parameters.

[0023] (3) After the constant temperature time ends, slowly cool it in the furnace to room temperature. To facilitate comparison of the heating effect, after taking it out, test its CIE-Lab data and ultraviolet-visible diffuse reflection curve at the same position. Test three points each time and compare them with the average value.

[0024] The purity of the potassium permanganate powder used in the present invention is not less than 88%.

[0025] Example 1 This example provides a method for oxidizing and heating a greyish-green jadeite to change its color to a red jadeite. The specific steps are as follows: S1. Grind and polish the greyish-green jadeite sample to be processed. S2. Heat the greyish-green jadeite sample obtained in step S1 and potassium permanganate for a preset time, and obtain a red jadeite after cooling. The heating conditions are: at a heating rate of 2 °C / min, heat from room temperature to 450 °C and keep warm for 6 h. The addition amount of the potassium permanganate powder is about 2 times the volume of the greyish-green jadeite sample. The greyish-green jadeite sample is 2.6 g, and the potassium permanganate powder is 3.6 g.

[0026] Example 2 It is basically the same as Example 1, except that the heating method is: at a heating rate of 5 °C / min, heat from room temperature to 450 °C and keep warm for 4 h. Example 3 It is basically the same as Example 1, except that the heating method is: at a heating rate of 5 °C / min, heat from room temperature to 400 °C and keep warm for 8 h. The addition amount of the potassium permanganate powder is about 2 times the volume of the greyish-green jadeite sample. The greyish-green jadeite sample is 5.2 g, and the potassium permanganate powder is 6 g.

[0027] Example 4 It is basically the same as Example 1, except that the heating method is as follows: heating from room temperature to 400 °C at a heating rate of 5 °C / min and holding for 6 h. The addition amount of potassium permanganate powder is about twice the volume of the greyish-green jadeite sample. The greyish-green jadeite sample is 5.2 g, and the potassium permanganate powder is 6 g.

[0028] Example 5 It is basically the same as Example 1, except that the heating method is as follows: heating from room temperature to 500 °C at a heating rate of 5 °C / min and holding for 4 h. The addition amount of potassium permanganate powder is about twice the volume of the greyish-green jadeite sample. The greyish-green jadeite sample is 5.2 g, and the potassium permanganate powder is 8 g.

[0029] Under the same parameter conditions, a comparison is made between the traditional heat treatment method and the heating method with the addition of other chemical reagents. The basic operations of heating include: First, the traditional heating method (without adding chemical reagents): (1) Grind, polish and clean the small pieces of jadeite to be treated. Use a spectrometer to test the CIE-Lab data and ultraviolet-visible diffuse reflection curve before heating.

[0030] (2) Place the greyish-green jadeite sample to be treated in a corundum crucible, and place a single crucible in a muffle furnace without adding any additional chemical reagents, and heat according to the set condition parameters.

[0031] (3) After the constant temperature time ends, slowly cool it to room temperature in the furnace. For the convenience of comparing the heating effect, after taking it out, test its CIE-Lab data and ultraviolet-visible diffuse reflection curve at the same position. Each time, test three points and compare them with the average value.

[0032] Secondly, the heating method with the addition of other chemical reagents (ferrous carbonate, ferrous oxide): (1) Grind, polish and clean the small pieces of jadeite to be treated. Use a spectrometer to test the CIE-Lab data and ultraviolet-visible diffuse reflection curve before heating.

[0033] (2) Place the greyish-green jadeite sample to be treated in a corundum crucible, cover the surface with a certain amount of chemical reagent powder to completely cover it, and then place the crucible in the muffle furnace hearth and heat according to the set condition parameters.

[0034] (3) After the constant temperature time ends, slowly cool it to room temperature in the furnace. For the convenience of comparing the heating effect, after taking it out, test its CIE-Lab data and ultraviolet-visible diffuse reflection curve at the same position. Each time, test three points and compare them with the average value.

[0035] Comparative Example 1 Basically the same as Example 1, except that potassium permanganate is not added.

[0036] Comparative Example 2 Basically the same as Example 2, except that potassium permanganate is not added.

[0037] Comparative Example 3 Basically the same as Example 4, except that potassium permanganate is not added.

[0038] Comparative Example 4 Basically the same as Example 4, except that ferrous carbonate powder is added, 2.8 g of grayish-green jadeite sample, and 3.8 g of ferrous carbonate powder.

[0039] Comparative Example 5 Basically the same as Example 4, except that ferrous oxide powder is added, 2.8 g of grayish-green jadeite sample, and 3.8 g of potassium permanganate powder.

[0040] Comparative Example 6 Basically the same as Example 5, except that potassium permanganate is not added.

[0041] Comparative Example 7 Basically the same as Example 5, except that ferrous carbonate powder is added, 3.3 g of grayish-green jadeite sample, and 6 g of ferrous carbonate powder.

[0042] Comparative Example 8 Basically the same as Example 5, except that ferrous oxide powder is added, 3.3 g of grayish-green jadeite sample, and 6 g of ferrous oxide powder.

[0043] Results and Analysis: Among the above-listed examples and comparative examples, four groups of comparisons are respectively formed between Example 1 and Comparative Example 1, Example 2 and Comparative Example 2, Example 4 and Comparative Examples 3, 4, 5, and Example 5 and Comparative Examples 6, 7, 8.

[0044] In terms of the optical physical essence, color is the subjective perception of the unabsorbed colored light reflected or transmitted by the surface of an object by the human eye. Due to the individual differences in the number, sensitivity, etc. of cone cells in the human eye retina, as well as the influence of light sources and the environment during the observation process, there are significant errors in color observation and description by the human eye alone, and it is difficult to ensure the accuracy and repeatability of the measurement results. The CIE system is a colorimetry system launched by the International Commission on Illumination, which can convert color perception into computable scientific parameters, solving the problems of objectivity and consistency in color description. Currently, the CIE1976Lab uniform color space is one of the most widely used methods for color quantitative analysis. This method consists of the planar chromaticity coordinate values a and b and the vertical axis L. The positive and negative directions of the a-axis represent red and green respectively, the positive and negative directions of the b-axis represent yellow and blue respectively, and the L-axis represents lightness.

[0045] The CIE-Lab means and differences collected at the same position before and after heating the samples are listed in Table 1. The data in the table shows that after heating, the a value of Example 1 increased by 7.55, which is higher than the chromaticity change of Comparative Example 1 (Δa value = 6.92); after heating, the a value of Example 2 increased by 6.75, which is higher than the chromaticity change of Comparative Example 2 (Δa value = 5.28). After heating, the a value of Example 4 increased by 6.46, while the a values of Comparative Examples 3, 4, and 5 increased by 5.42, 2.93, and 1.88 respectively. After heating, the a value of Example 5 increased by 9.73, and the a values of Comparative Examples 6, 7, and 8 increased by 7.76, 7.67, and 7.62 respectively. At the same time, the change in the b value is also worthy of attention. From the first group of comparisons, the yellow tone improvement of Comparative Example 1 is slightly more obvious (4.65 > 2.74). In the second group of comparisons, the yellow tone improvement range of Example 2 is significantly higher than that of Comparative Example 2 (4.87 > 0.42). In the third group of comparisons, the yellow tone of Example 4 is higher than that of the corresponding comparative examples (6.80 > 4.26, -1.06, -5.90). In the fourth group of comparisons, the results of Example 5 also reflect this phenomenon (10.35 > 7.26, 8.56, 2.42). The changes in CIE-Lab values before and after heating indicate that the potassium permanganate-assisted heating method has a significant effect on enhancing the red tone during the heat treatment process and also makes a certain contribution to the improvement of the yellow tone.

[0046] To reflect the degree of closeness between the heating effect and natural red jadeite, 5 samples of natural red jadeite with relatively typical colors were obtained from the GIC Vocational Education Center of the School of Jewelry, China University of Geosciences (Wuhan) for colorimetry data collection. Their CIE-Lab parameters are shown in Table 2, and the appearance characteristics are shown in the appendix Figure 14 . The chromaticity value ranges of the 5 natural red jadeite samples are: L ∈ (27.70, 36.53), a ∈ (7.56, 10.24), b ∈ (10.43, 17.45), and the mean values are: L = 33.87, a = 8.74, b = 13.41. Compared with each of the above specific embodiments, the L values of all embodiments are greater than those of the natural red jadeite samples, indicating that the artificially heated samples have higher lightness. In addition, from the red and yellow tones reflected by the a and b values, the a and b values of Example 5 are close to those of the natural samples, and the b value of Example 3 is close to that of the natural samples. The set parameters of other embodiments reflect that heating treatment at a higher temperature and maintaining a constant temperature for a certain period of time will play a more significant and effective role in color improvement.

[0047] Table 1. CIE-Lab data before and after heating for each specific embodiment and comparative example

[0048] Table 2. CIE-Lab data of relatively typical natural red jadeite.

[0049]

[0050] The ultraviolet-visible diffuse reflectance spectra of each heating method were plotted using Origin software. The ultraviolet-visible diffuse reflectance spectra of each example and comparative example are shown in Figure 15 . The figure shows that the ultraviolet-visible diffuse reflectance test results of each heating method are consistent, all showing certain absorption in the blue-violet-green region (380 - 570 nm) and a broad reflection peak in the orange-yellow-red region (570 - 750 nm). According to the complementary color theory, the human eye can observe the mixed color of the unabsorbed light. After the sample absorbs the light in the blue-violet-green region, the remaining light in the orange-yellow-red region is mixed, showing a yellow-red tone. The original ultraviolet-visible diffuse reflectance spectra of each example and comparative example have multiple overlapping spectral peaks at fine positions, which are not easy to observe and compare ( Figure 15 ). The first derivative can enhance the signal mathematically and show minute fluctuations. Taking the first derivative of the original curve and comparing the positions of the characteristic peaks of different heating methods can effectively reflect the types and concentration changes of iron oxides before and after heating. According to research, the characteristic peaks of goethite are the main peak at 535 nm and the secondary peak at 435 nm, and the characteristic peak of hematite is between 560 - 580 nm, showing a single-peak form. When the concentration increases, the main peak positions of goethite and hematite will shift towards the high-wavelength direction. However, when goethite and hematite coexist, the peak position of hematite will shift towards the short-wavelength direction, and this shift will also cause the main peak of goethite to be masked.

[0051] Combined with Figure 16The first-order derivative spectra of the ultraviolet-visible diffuse reflectance shown. The characteristic peak positions of Example 1 are at 560 and 582 nm, both within the hematite range. For Comparative Example 1, the characteristic peak position is at 550 nm. Although the peak intensity is slightly higher than that of Example 1, its characteristic peak position is at a shorter wavelength. Therefore, the conversion process of goethite to hematite is not complete, and there is unconverted goethite, which affects the range of its main peak. The characteristic peak position and intensity of Example 2 are both greater than those of Comparative Example 1, indicating that the heating effect of Example 2 is more significant than that of Comparative Example 2. The characteristic peak positions of these two examples both appear in the intermediate region between goethite and hematite, probably due to a slightly shorter heating time. The peak position and intensity shown in Example 4 are higher than those of the traditional heating method and Comparative Examples 4 and 5 with added ferrous carbonate and ferrous oxide. Especially after the powder-covered heating process, the first-order derivative spectral peak shapes of Comparative Examples 4 and 5 are flat, indicating a relatively low conversion amount of hematite. Example 5 shows a relatively high first-order derivative spectral peak intensity, covering a large area in the 550 - 750 nm range. The absorption in the 580 - 740 nm band was once considered to be the charge transfer spectrum of Fe 2+ —Fe 3+ , and some scholars also believe it is the combined effect of Fe 2+ ( 5 T2)+Fe 3+ ( 6 A1)→Fe 2+ ( 5 E)+Fe 3+ ( 6 A1). The unique spectral peak shape of Example 5 indicates that the process of potassium permanganate-assisted heating achieved the conversion of Fe 3+ . Since the color development degree of hematite is more obvious than that of goethite, a small amount of hematite in the sample can show a characteristic red tone. The high concentration of hematite in Example 5 will make it show a deeper red. Comparative Example 6 without adding any chemical reagents has a sharp spectral peak at 565 nm, but there is no shift towards the high-wavelength direction, indicating that the heating effect is inferior to the potassium permanganate-assisted heating method. At the same time, Comparative Examples 7 and 8 with added ferrous carbonate and ferrous oxide still show spectral peaks in the intermediate region between goethite and hematite under the same set parameters as Example 5, indicating that the covered heating method may hinder the transfer of oxygen to the sample, and the conversion of goethite to hematite is incomplete, that is, both goethite and hematite exist simultaneously, making the characteristic peak position of hematite at a shorter wavelength.

[0052] In summary, based on the hematite peak positions indicated by the CIE-Lab parameters and the first derivative spectra of ultraviolet-visible diffuse reflection, it can be determined that the auxiliary heat treatment effect of potassium permanganate is superior to that of traditional heat treatment or heat treatment with ferrous carbonate or ferrous oxide coating. While increasing the oxygen concentration and boosting the rate of the oxidation reaction, potassium permanganate can significantly enhance the red tone and to some extent the yellow tone in the heating effect, verifying the role of the present invention in improving the heating effect of heat-treated red jadeite.

[0053] Without conflict, the above-mentioned embodiments and the features in the embodiments in this article may be combined with each other.

[0054] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for changing the color of grayish-green jadeite to red jadeite by oxidation heating, characterized in that, The following steps are involved: S1. Grind and polish the gray-green jadeite sample to be processed. S2. Heat the gray-green jadeite sample obtained in step S1 and potassium permanganate together for a preset time, and obtain red jadeite after cooling.

2. The method according to claim 1, characterized in that The purity of the potassium permanganate is not less than 88%.

3. The method according to claim 2, characterized in that, The mass ratio of the gray-green jadeite sample to potassium permanganate is 1: (1.15~1.81).

4. The method according to claim 3, wherein The heating process is as follows: heating from room temperature to 400-500° C. at a heating rate of 2-5° C. / min, and keeping the temperature for 4-8 hours.

5. The method according to claim 2, characterized in that The heating equipment is a muffle furnace or a tubular furnace.

6. The method according to claim 1, wherein The gray-green jadeite sample is natural jadeite.

7. The method according to any one of claims 1-6, characterized in that, The CIE-Lab data of the red jadeite showed that the L values were all greater than those of natural red jadeite samples.

8. The method according to any one of claims 1 to 6, wherein The refractive index of the red jadeite is between 1.66 and 1.

67.

9. The method according to any one of claims 1 to 6, wherein The first-order derivative ultraviolet-visible diffuse reflectance spectrum data of the red jadeite shows an absorption peak at 540~580nm.

10. Use of the method according to any one of claims 1 to 6 in preparing jewelry, artwork or collectibles.

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