JP7555265B2 - Inorganic iron-containing glass composition for use in hydroponics - Google Patents

Description

The present invention relates to an inorganic iron-containing glass composition. More specifically, the present invention relates to an inorganic iron-containing glass composition that contains _P2O5 and _K2O as a _glass composition and FeO as inorganic iron, and is used as a fertilizer in hydroponic culture and nutrient solution culture in general.

Hydroponics is a method of growing plants without using any soil, using a solution (nutrient solution) containing the nutrients necessary for growth. In hydroponics, the roots of the plants are immersed in the nutrient solution, and the plants grow by absorbing the nutrients through their roots. Because hydroponics does not require soil replacement, it is less likely to get dirty, and it is easy to grow flowers, vegetables, and herbs even in indoor spaces.

On the other hand, when comparing hydroponics with soil cultivation, hydroponics uses water that contains less nutrients than soil, so the plants take in less nutrients and this can inhibit plant growth. For this reason, the nutrient solution is important in hydroponics, and fertilizers that can provide this nutrient solution are also important.

Fertilizers for hydroponics must contain a good balance of all the nutrients essential for crops, and the lack of even one of them will impair growth. Among these nutrients, iron has a tendency to precipitate in water. In particular, iron ions in the nutrient solution are highly susceptible to precipitation when combined with phosphate ions or hydroxide ions. In soil cultivation, the precipitated iron can be redissolved and absorbed by the roots, but in hydroponics, the iron is washed away by the water and the plant cannot absorb it. In other words, iron deficiency rarely occurs in soil cultivation, but it easily occurs in hydroponics. To address this issue, fertilizers for hydroponics always contain synthetic chelate iron, such as iron EDTA and iron DTPA, to prevent iron precipitation.

For example, Patent Document 1 discloses a hydroponic cultivation method in which leafy vegetables are grown in a culture solution normally formulated for hydroponic cultivation, and from 1 to 4 days before harvest, a high-iron-containing culture solution containing more than 0.36 mM and not more than 6.0 mM iron EDTA is used.

Patent No. 6487304

The hydroponic cultivation method described in Patent Document 1 discloses that a nutrient solution containing a large amount of iron is prepared by dissolving the fertilizer EDTA iron in water, and the roots of leafy vegetable plants are immersed in the nutrient solution, which allows the leafy vegetable plants to absorb a large amount of iron, resulting in sufficient plant growth and enabling the cultivation of leafy vegetables that are rich in iron.

On the other hand, although a large amount of iron EDTA can be dissolved in water, if too much is added, it can cause growth problems in plants, so it is necessary to properly adjust the amount of iron EDTA added each time. For this reason, it would be ideal to have a hydroponic fertilizer that dissolves iron slowly in water, eliminating the need to add iron EDTA periodically and preventing the nutrient solution from containing too much iron.

As a result of intensive research in light of the above problems, the inventors discovered that by using a specific glass composition containing inorganic iron as fertilizer for hydroponics, the iron derived from the inorganic iron slowly dissolves in water, which led to the present invention.

The invention according to claim 1 relates to an inorganic iron-containing glass composition comprising (a) 36 mol% to ₄₄ mol% _{of P2O5 ,} (b) 36 mol% to 44 mol% of K2O, and (c) 18 mol% to 20 mol% of FeO, further comprising (f) a reducing agent not containing a nitrogen compound, and having a molar ratio of _P2O5 / _K2O of 0.8 to 1.2, the inorganic iron-containing glass composition being used as a fertilizer in hydroponic culture and nutrient solution culture in general , and maintaining a divalent iron concentration in the nutrient solution of 1.2 ppm or more for about three weeks .

The invention according to claim 2 relates to the inorganic iron-containing glass composition according to claim 1, further comprising (d) 0.01 mol% to 0.5 mol% CuO, and/or (e) 0.01 mol% to 0.5 mol% ZnO.

The invention according to claim 3 relates to the inorganic iron-containing glass composition according to claim 1 or 2 , wherein the inorganic iron-containing glass composition has a flake shape.

According to the invention of claim 1, there is provided an inorganic iron-containing glass composition containing (a) 36 mol% to 44 mol% P ₂ O ₅ , (b) 36 mol% to 44 mol% K ₂ O 2 and (c) 18 mol% to 20 mol% FeO 2 , with a molar ratio of P ₂ O ₅ /K ₂ O of 0.8 to 1.2, and the inorganic iron-containing glass composition is used as a fertilizer in hydroponic culture and general nutrient solution culture, so that the iron content derived from the inorganic iron slowly dissolves in water and the iron concentration in the nutrient solution can be maintained for a long period of time. Therefore, it is possible to provide a fertilizer for hydroponic culture and general nutrient solution culture that does not require the periodic addition of iron EDTA and does not cause the nutrient solution to have too much iron. In addition, by using the inorganic iron-containing glass composition as a fertilizer, the burden on the grower in hydroponic cultivation of plants is reduced, and the iron is appropriately contained in the plants, making it possible to carry out hydroponic cultivation and nutrient solution cultivation in general without the risk of the plants suffering from growth disorders.
In addition, since the glass further contains a reducing agent (f) for maintaining a reduced state when the glass is melted, the iron is reduced and the skeleton of the glass is appropriately cut, whereby the iron in the inorganic iron-containing glass composition can be slowly dissolved in water, and a fertilizer for hydroponic culture and general nutrient solution culture can be provided in which the nutrient solution does not contain too much iron.

According to the invention of claim 2, the inorganic iron-containing glass composition further contains (d) 0.01 mol% to 0.5 mol% CuO, and/or (e) 0.01 mol% to 0.5 mol% ZnO, so that copper and/or zinc, which are important components for plant growth, can be dissolved in water, making hydroponic cultivation of plants more comfortable. This makes it possible to eliminate the use of copper EDTA and/or zinc EDTA during hydroponic cultivation or reduce the amount used, eliminating the need to periodically add copper EDTA and/or zinc EDTA or reducing the number of times they are used. Therefore, it is possible to provide a fertilizer that enables comfortable hydroponic cultivation without the risk of the copper and zinc concentrations in the nutrient solution suddenly increasing.

According to the invention of claim 4, the inorganic iron-containing glass composition has a flake shape, so it does not solidify in the nutrient solution, and the iron in the inorganic iron-containing glass composition can be slowly dissolved in water, and a fertilizer for hydroponic cultivation can be provided that does not cause the nutrient solution to have too much iron.

FIG. 1 is a diagram showing iron concentrations in nutrient solutions obtained by dissolving a fertilizer containing an inorganic iron-containing glass composition according to an embodiment of the present invention and a fertilizer containing an EDTA-iron-containing glass composition according to a comparative example in water when hydroponically cultivating lettuce. FIG. 1 is a photograph of lettuce harvested after hydroponic cultivation using a nutrient solution in which a fertilizer containing an inorganic iron-containing glass composition according to an embodiment of the present invention and a fertilizer containing an EDTA-iron-containing glass composition according to a comparative example are dissolved in water.

A preferred embodiment of the inorganic iron-containing glass composition according to the present invention (hereinafter also simply referred to as the "inorganic iron-containing glass composition") will be described.

The present inorganic iron-containing glass composition contains P ₂ O ₅ (diphosphorus pentoxide) and K ₂ O (potassium oxide), and potassium phosphate, ammonium phosphate, potassium carbonate, etc. can be used as the melting raw material thereof.

P ₂ O ₅ and K ₂ O play a role as a skeleton in the inorganic iron-containing glass composition, and can determine the shape of the fertilizer and adjust the dissolution rate of the fertilizer components in water. Therefore, by making the inorganic iron-containing glass composition into a specific composition, the dissolution rate of the iron in water can be adjusted and the iron concentration in the nutrient solution can be maintained for a long period of time, eliminating the need to periodically add EDTA iron as in the past, and allowing iron to be stably supplied to crops without using organic synthetic chelated iron.

The content of P ₂ O ₅ in the glass composition can be, for example, within the range of 36 mol% to 44 mol%. If the content of P ₂ O ₅ is less than 36 mol%, fertilizer components such as iron are too dissolved in water, and if the content of P ₂ O ₅ is more than 44 mol%, fertilizer components such as iron are difficult to dissolve in water. Moreover, it is more preferable that the content of P ₂ O ₅ in the glass composition is 39 mol% to 41 mol%, so that fertilizer components such as iron can be slowly dissolved in water and the iron concentration in the nutrient solution can be maintained for a long period of time.

The content of K ₂ O in the glass composition can be, for example, within the range of 36 mol% to 44 mol%. If the content of K ₂ O is less than 36 mol%, fertilizer components such as iron are difficult to dissolve in water, and if the content of K ₂ O exceeds 44 mol%, fertilizer components such as iron are excessively dissolved in water. It is more preferable that the content of K ₂ O in the glass composition is 39 mol% to 41 mol%, so that fertilizer components such as iron can be slowly dissolved in water and the iron concentration in the nutrient solution can be maintained for a long period of time.

The molar ratio of P ₂ O ₅ /K ₂ O in the glass composition of the present inorganic iron-containing glass composition can be, for example, within the range of 0.8 to 1.2. If the molar ratio of P ₂ O ₅ /K ₂ O is less than 0.8, the skeleton of the glass becomes weak, and fertilizer components such as iron are too easily dissolved in water. If the molar ratio of P ₂ O ₅ /K ₂ O exceeds 1.2, the skeleton of the glass becomes too strong, and fertilizer components such as iron are difficult to dissolve in water. It is more preferable that the molar ratio of P ₂ O ₅ /K ₂ O in the glass composition is within the range of 0.9 to 1.1, and fertilizer components such as iron can be slowly dissolved in water, and the iron concentration in the nutrient solution can be maintained for a long period of time.

The present inorganic iron-containing glass composition does not need to contain Na ₂ O as a glass composition. Generally, Na ₂ O is sometimes contained in order to make glass easier to melt, but sodium is not essential for plant growth and can have a harmful effect if contained in a large amount, so glass that does not contain Na ₂ O is suitable for plant cultivation.

This inorganic iron-containing glass composition contains only inorganic iron, and does not contain synthetic chelated iron such as iron EDTA. Vitrification prevents the iron from dissolving in water all at once. In hydroponic cultivation, iron is an essential fertilizer component for plant growth, and if the iron is depleted, the plants being grown hydroponically may wither and die. This death of the plants occurs because there is a large amount of iron in the soil, but almost no iron in the water.

In the present inorganic iron-containing glass composition, the content of FeO can be, for example, within the range of 18 mol% to 20 mol%. The content of FeO in the inorganic iron-containing glass composition greatly affects the solubility of iron in water. If the content of FeO is low, the skeleton of the glass is weak and a lot of iron is dissolved, and if the content of FeO is high, the skeleton of the glass is too strong and iron is difficult to dissolve. If the content of FeO is less than 18 mol%, the solubility of iron in water is high and the iron concentration in the nutrient solution cannot be maintained for a long period of time. In addition, the inorganic iron-containing glass composition is easily altered in air. On the other hand, if the content of FeO exceeds 20 mol%, the inorganic iron-containing glass composition is less likely to be altered in air, but the solubility of iron in water is low and the iron concentration in the nutrient solution is low. Furthermore, it is more preferable that the FeO content is within the range of 18.5 mol% to 19.6 mol%, which is less likely to deteriorate in air and has good solubility of iron in water, allowing the iron concentration in the nutrient solution to be maintained for a long period of time.

The inorganic iron-containing glass composition may further contain copper as a fertilizer component. By containing copper in the inorganic iron-containing glass composition, the copper component can be dissolved in water, and a fertilizer for hydroponic cultivation and general nutrient solution cultivation that can supply the copper component to plants can be provided.

The copper content in the inorganic iron-containing glass composition can be, for example, in the range of 0.01 mol% to 0.5 mol% as CuO. If the CuO content is less than 0.01 mol%, the copper concentration when the inorganic iron-containing glass composition is dissolved in water will be low, and a fertilizer that will sufficiently grow plants will not be provided. On the other hand, if the CuO content exceeds 0.5 mol%, the copper concentration when the inorganic iron-containing glass composition is dissolved in water will be high, and there is a risk of plant growth being impaired. In addition, it is more preferable that the CuO content is in the range of 0.05 mol% to 0.15 mol%, and the copper component dissolves slowly in water, allowing the copper concentration in the nutrient solution to be maintained for a long period of time.

The inorganic iron-containing glass composition may further contain zinc as a fertilizer component. By containing zinc in the inorganic iron-containing glass composition, the zinc component can be dissolved in water, and a fertilizer for hydroponic cultivation and general nutrient solution cultivation that can supply the zinc component to plants can be provided.

The zinc content in the inorganic iron-containing glass composition can be, for example, within the range of 0.01 mol% to 0.5 mol% as ZnO. If the ZnO content is less than 0.01 mol%, the zinc concentration when the inorganic iron-containing glass composition is dissolved in water will be low, making it impossible to provide a fertilizer that will sufficiently grow plants. On the other hand, if the ZnO content exceeds 0.5 mol%, the zinc concentration when the inorganic iron-containing glass composition is dissolved in water will be high, which may cause plant growth disorders. It is more preferable that the ZnO content is within the range of 0.05 mol% to 0.15 mol%, and the zinc component dissolves slowly in water, allowing the zinc concentration in the nutrient solution to be maintained for a long period of time.

By adding a reducing agent and melting the inorganic iron-containing glass composition, the glass skeleton can be weakened, the dissolution rate of the iron component in the inorganic iron-containing glass composition in water can be adjusted, and the iron concentration in the nutrient solution can be maintained for a long period of time, making the composition suitable for use as a fertilizer for hydroponic cultivation. The reducing agent can be, for example, various organic substances such as coal and coke, or natural gas. When coke is used, 0.01 wt% to 5.0 wt% is preferable.

One example of the inorganic iron-containing glass composition is an inorganic iron-containing glass composition containing 36 mol% to 44 mol% P ₂ O ₅ , 36 mol% to 44 mol% K ₂ O, and 18 mol% to 20 mol% FeO, with a molar ratio of P ₂ O ₅ /K ₂ O of 0.8 to 1.2. Since the iron content derived from the inorganic iron slowly dissolves in water, this inorganic iron-containing glass composition can maintain the iron concentration in the nutrient solution for a long period of time, and can be suitably used as a fertilizer in hydroponic cultivation.

Another example of the inorganic iron-containing glass composition may be an inorganic iron-containing glass composition that contains 39 mol% to 41 mol% P ₂ O ₅ , 39 mol% to 41 mol% K ₂ O , 18.5 mol% to 19.6 mol% FeO , 0.05 mol% to 0.15 mol% CuO, and 0.05 mol% to 0.15 mol% ZnO, has a molar ratio of P ₂ O ₅ /K ₂ O of 0.9 to 1.1, and is melted by adding 2.0 wt% to 2.5 wt% of coke during melting of the glass. Since the inorganic iron-containing glass composition slowly dissolves iron derived from inorganic iron in water, the iron concentration in the nutrient solution can be maintained for a long period of time, and the composition can be suitably used as a fertilizer in hydroponic cultivation.

The shape of the inorganic iron-containing glass composition is not particularly limited, but it is preferable to use one in the form of flakes. For example, by using an inorganic iron-containing glass composition in the form of flakes with a size of 1 mm to 4 mm in hydroponic cultivation, it can be used without solidifying in the nutrient solution. An inorganic iron-containing glass composition in the form of flakes can be used more suitably as a fertilizer for hydroponic cultivation than a powdered inorganic iron-containing glass composition.

The inorganic iron-containing glass composition is produced, for example, by placing the raw materials for the above-mentioned glass composition and a reducing agent in a crucible, melting them at 1250°C, vitrifying them, and then rapidly cooling them.

In the production of this inorganic iron-containing glass composition, the melting temperature can be appropriately set to an optimal value depending on the type of inorganic iron-containing glass composition being produced.

The effects of the present invention will be made clearer by showing examples of the inorganic iron-containing glass composition according to the present invention below. However, the present invention is not limited to the following examples.

[Example]
(Preparation of Inorganic Iron-Containing Glass Compositions with Copper and Zinc)
_P2O5 and _K2O as glass components, FeO, CuO, ZnO as fertilizer components, and coke _as a reducing agent were mixed and added to a crucible. The crucible was then heated and melted in a kiln at 1250°C to be vitrified. The crucible was removed from the kiln, and the molten material was poured onto a water-cooled stainless steel roll and quenched to obtain an inorganic iron-containing glass composition in the form of _flakes . The component ratios, _P2O5 / _K2O ratio, and frit size of the inorganic iron-containing glass composition are shown in Table 1.

[Comparative Example]
(Iron EDTA, Copper EDTA, Zinc EDTA)
Fe(III)-EDTA was used as the iron fertilizer component, Cu(II)-EDTA as the copper fertilizer component, and Zn(II)-EDTA as the zinc fertilizer component.

(Preparation of nutrient solution for hydroponic cultivation)
The nutrient solution used in hydroponic cultivation is insufficient if it contains only iron as a fertilizer component, and plants cannot be grown. Therefore, in order to supplement the fertilizer components, the following fertilizers were prepared and used in combination to grow lettuce.

A mixed fertilizer for hydroponic culture (A) containing each fertilizer component but not containing iron, nitrate nitrogen and Ca(NO ₃ ) ₂ (calcium nitrate) (B) as a calcium component were dissolved in water to prepare a fertilizer for hydroponic culture.

150 g of hydroponic mixed fertilizer (A) was dissolved in 1 L of water to prepare a concentrated solution of (A). Similarly, 100 g of (B) was dissolved in another 1 L of water to prepare a concentrated solution of (B).

The concentrated solution of the prepared hydroponic mixed fertilizer (A) and the concentrated solution of (B) were mixed in a 1:1 ratio to prepare a 220-fold diluted solution. The inorganic iron-containing glass composition of the Example or the iron EDTA of the Comparative Example was added to the prepared 220-fold diluted solution to prepare a hydroponic nutrient solution. The ratios of the guaranteed components and effect expression promoters of the hydroponic mixed fertilizer used to prepare the nutrient solution are shown in Table 2.

(Hydroponic cultivation test of lettuce using inorganic iron-containing glass composition and ferric EDTA-containing nutrient solution)
In order to confirm the fertilizing effect of the inorganic iron-containing glass composition of the embodiment, the hydroponic culture solution was prepared by the above-mentioned method, and lettuce was hydroponically grown. As a comparison, lettuce was hydroponically grown using the EDTA iron-containing nutrient solution of the comparative example.

The hydroponic cultivation test was carried out using Yasai-e (registered trademark of M-type Hydroponic Research Institute Co., Ltd.), a closed plant cultivation unit. Hydroponic cultivation was carried out by flooded liquid culture, and the cultivation area was 5.4 ^m2 (320 plants). 350 L of hydroponic nutrient solution was used for each experiment, and the inorganic iron-containing glass composition was added in the example, and ferric EDTA was added in the comparative example. The nutrient solution was circulated in multiple stages, and a white LED was used as the light source.

In the hydroponic cultivation test of lettuce using the nutrient solutions of the examples and comparative examples, the lettuce was transplanted 10 days after sowing and harvested 27 days after transplanting.

When using the Example, the inorganic iron-containing glass composition was added only three days before transplantation, and no iron fertilizer was added thereafter. On the other hand, the nutrient solution of the Comparative Example was used on the first day, and then 0.8 L of EDTA iron-containing concentrate was added on the 20th day after transplantation and 0.8 L of EDTA iron-containing concentrate on the 24th day after transplantation to maintain the iron concentration.

(Investigation of iron concentration in nutrient solution)
During the hydroponic cultivation of lettuce, the iron concentration in the nutrient solution in each test plot was investigated and the average value was calculated. The results are shown in Figure 1.

(Growth and yield survey)
After the cultivation test was completed, lettuce was harvested from each test plot, and the weight, standard deviation, leaf length, yield, and yield ratio after growth were examined, and the average values were calculated. The results are shown in Table 3. A photograph of the harvested lettuce is shown in Figure 2.

(Inorganic content of lettuce)
After the cultivation test was completed, the lettuce in each test area was harvested, and the inorganic component contents and water contents after growth were examined and the average values were calculated. The results are shown in Table 4.

In both the test plots of the Example and Comparative Example, lettuce of sufficient weight and shape was harvested. This is also evident from the results in Table 3 and Figure 2. Furthermore, the results in Table 4 show that there was no significant difference in the inorganic component content of the harvested lettuce between the test plots of the Example and Comparative Example.

However, differences in the effectiveness of the nutrient solution were observed between the test plots of the examples and the comparative examples. The details of these differences are described below.

Figure 1 shows the results of the investigation of the iron concentration in the nutrient solution. In the experimental plots of the embodiment, the initial iron concentration was low, but the iron concentration gradually increased as the plants grew, and although the iron concentration decreased from 14 days after transplantation, the iron concentration was maintained at 1.2 ppm or more until just before harvest. In other words, it was found that the iron concentration in the nutrient solution can be maintained at 1.2 ppm or more for about three weeks by the first addition of the inorganic iron-containing glass composition. In hydroponic cultivation of plants, sufficient growth can be expected by maintaining the iron concentration in the nutrient solution at 1.2 ppm or more, and therefore it was found that the nutrient solution of the embodiment is effective in hydroponic cultivation.

On the other hand, in the comparative test plot, the iron concentration in the nutrient solution could not be maintained at 1.2 ppm or more in the latter half of the growth period, and it was necessary to add iron EDTA twice more. This is because in the comparative test plot, the entire amount of iron EDTA was dissolved in the nutrient solution from the beginning, and iron absorbed by the plants or precipitated in the nutrient solution had to be constantly replenished. In other words, in the comparative test plot, in order to maintain the iron concentration in the nutrient solution at 1.2 ppm or more, it was found that iron EDTA had to be added a total of three times during the one-month hydroponic cultivation test period. Also, if one were to try to maintain the iron concentration in the nutrient solution at 1.2 ppm or more with a single addition of iron EDTA, the initial iron concentration in the nutrient solution would have to be high, but iron EDTA had to be added in several doses because there was a risk of phytotoxicity of EDTA to the plants.

The results of the hydroponic cultivation test of lettuce described above show that the inorganic iron-containing glass composition of the embodiment is effective as a fertilizer for hydroponic cultivation. Therefore, it was found that the inorganic iron-containing glass composition of the embodiment can be suitably used widely as a fertilizer for hydroponic cultivation that does not require the periodic addition of iron EDTA and does not cause the nutrient solution to have too much iron.

In the hydroponic cultivation test of lettuce described above, when the inorganic iron-containing glass composition containing added copper and zinc of the embodiment was used, the copper and zinc contents in the lettuce increased compared to when copper EDTA and zinc EDTA of the comparative example were used, as shown in the results in Table 4.

When hydroponic cultivation is performed using the examples, it is believed that the amounts of copper EDTA and zinc EDTA used can also be reduced. This shows that the inorganic iron-containing glass composition to which copper and zinc have been added according to the examples can be used as a more suitable fertilizer for hydroponic cultivation.

According to the inorganic iron-containing glass composition of the present invention, the inorganic iron-containing glass composition contains (a) 36 mol% to 44 mol% of P ₂ O ₅ , (b) 36 mol% to 44 mol% of K ₂ O , and (c) 18 mol% to 20 mol% of FeO , and the molar ratio of P ₂ O ₅ /K ₂ O is 0.8 to 1.2. The inorganic iron-containing glass composition can be used as a fertilizer in hydroponic cultivation and nutrient solution cultivation in general, and the iron content derived from the inorganic iron slowly dissolves in water, so that the iron concentration in the nutrient solution can be maintained for a long period of time. Therefore, it is possible to provide a fertilizer for hydroponic cultivation and nutrient solution cultivation in general, which does not require the periodic addition of EDTA iron and does not cause the iron content in the nutrient solution to become too high. In addition, by using the inorganic iron-containing glass composition as a fertilizer, the burden on the grower in hydroponic cultivation of plants can be reduced, and the plants can be appropriately contained with iron, making it possible to perform hydroponic cultivation without the risk of causing growth disorders in the plants.

Therefore, the inorganic iron-containing glass composition of the present invention can be suitably and widely used as a fertilizer for hydroponic cultivation and general nutrient solution cultivation, which does not require the periodic addition of iron EDTA and does not cause the nutrient solution to have too much iron.

Claims (3)

(a) P ₂ O ₅ 36 mol% to 44 mol%,
(b) 36 mol% to 44 mol% _K2O ; and (c) 18 mol% to 20 mol% FeO;
(f) further comprising a reducing agent that does not contain nitrogen compounds;
The molar ratio of P ₂ O ₅ /K ₂ O is 0.8 to 1.2, and the inorganic iron-containing glass composition is used as a fertilizer in hydroponic culture and nutrient solution culture in general , and the iron in these nutrient solutions is An inorganic iron-containing glass composition that maintains a valent iron concentration of 1.2 ppm or more for about three weeks . The inorganic iron-containing glass composition comprises:
2. The inorganic iron-containing glass composition of claim 1, further comprising: (d) 0.01 mol % to 0.5 mol % CuO; and/or (e) 0.01 mol % to 0.5 mol % ZnO. The inorganic iron-containing glass composition according to claim 1 or 2 , wherein the inorganic iron-containing glass composition is in the form of flakes.