As we all know, red is one of the three primary colors of color. Why is there such a big difference between the same red pigment you use and the master? In addition to color sensitivity, composition and other factors that test the painter's skills, there is also the understanding of various materials, so in the following time, Mr. Lu will talk to you.
We have talked about many inorganic colors in the previous pigment articles, and today's article will focus on analyzing these red organic colors with you.
Before we get to the main topic, let's first look at the knowledge of organic pigments.
Organic pigments
Organic pigments are colored materials with pigment properties made of organic compounds. They are also a class of organic compounds with insoluble and high coloring power. The common types are azo pigments, pigment precipitates and quinacridone pigments.
However, the light resistance and durability of organic pigments are generally not as good as inorganic pigments, which is the shortage of organic pigments.
Next, we will get to the main topic today! First of all, we will start with the more arguable pyrrole and pyrrole diketone pigments, also known as DPP pigments, which belong to a new generation of high performance organic pigments, with perfect symmetry of molecular structure and hydrogen bonding between molecules.
China Red
For example, PR254, which corresponds to the Chinese red in Rubens' oil painting artist grade, is a classic color with Chinese characteristics, just like its name, and there is a jingle in the pigment industry: "Yellow can't get on 180, red can't get on 254". This also shows the important status of this pigment. Except for the halogen content, the performance of this pigment is quite good in other aspects.
The following diagram shows its molecular structure
Molecular formula C18H10Cl2N2O2
The drying time of this pigment is about 96±5 hours, it is a semi-transparent pigment with five-star weather resistance, so it can be used either alone or mixed with other pigments in the use of the pigment. Here are a few experiments to show you its relevant pigment properties.
First, let's take a look at its coloring power test. We add different proportions of titanium white separately, and then compare its single color. The standard color we used here is Rubens Artist Grade Titanium White.
Through the experiment we can find that this color still has a high color saturation, and the space for descendable color is good. Painters can adjust the color according to their needs.
Then the next is the different effects presented after adding titanium white, zinc white, zinc titanium white and lead white respectively.
Here we have also inquired about the materials used in some of the oil paint brands, as shown in the table below, so you can have a brief understanding.
Of course there are many other red pigments that are not introduced here, such as: PR3/4 /21/ 48-2/ 48:3/ 170/ 261 (low to medium grade, transparent/ translucent) These pigments are more common in college grade oil paints, while in artist grade oil paints or mostly medium to high grade pigments are more common, such as. PR254/255/209/177/122/207 and so on. This is one of the reasons for the price difference between different materials. [Take Chinese red as an example, in the artist level generally use the sunlight resistance level eight PR254, while in some college level will use the sunlight resistance level 6 or 5 PR21 or PR48 instead, and PR254 is more expensive than PR21 or PR48 dozens of times, even if some college level will use PR254, it is not pure, but added other fillers.
College Grade - Commonly Used Colorants
Bd 2-naphthol pigment: C.I. Pigment Red 4
Be 2-naphthol pigment: C.I. Pigment Red 49:1 C.I. Pigment Red 53:1
Bf Chromophenol AS pigment: C.I. Pigment Red 21 C.I. Pigment Red 170
Bg 2,3-acid and pigment precipitates: C.I. Pigment Red 48:1 C.I. Pigment Red 48:2
Add a comparison table of pigment colors of Old Dutch and Rubens
The names of painting pigments include generic and special names. Most of the pigments have generic names based on the hue or composition of the color, such as lemon yellow, cadmium red, and so on. There are also names based on the place of origin or trade such as Venetian Red, Indian Red, etc. There are also many that are named after masters of the art or inventors, such as Van Dyke Brown, etc. Some manufacturers also name their special pigments according to their own brands, so this has led to inconsistencies in the names of pigments].
Vermilion
Among all the red organic colors, we often use vermilion, the drying time of vermilion is similar to Chinese red, also belongs to a translucent pigment, its weather resistance is not as good as Chinese red pigment, the weather resistance is four stars, in the use of the general is not recommended for a large area of laying color use, can consider and other pigment blend use.
Some painters may have experienced the phenomenon of color flip after painting a large area of vermilion red and then white, which is because the granularity of the pigment is not fine enough, and then the dry oil in the pigment can not be wrapped, which leads to the phenomenon of color flip. So when we buy vermilion pigment, we can observe its paste fineness first, when the fineness is not quite enough, we can avoid this kind of situation in advance when using it, and reduce the phenomenon of color flip of the painting.
Here we also add titanium white, lead white, zinc white and zinc titanium white to see how its color changes.
Xisu Red
Traditionally, alizarin red is extracted from the roots of the natural plant Alizarin. Although the natural alizarin red is strong in coloring, it is less durable and the alizarin red used nowadays is basically a synthetic red pigment of the onion quinone series. There are some gaps between its hue and the natural alizarin red, and it is usually not recommended to apply thickly and individually over a large area in use.
Its drying time is also 96±5 hours, it is a semi-cover pigment, with relative density of 1.45-1.53 and oil absorption of 55-62(g/100g), which is a low oil absorption oil pigment, its molecular formula is C28H16N2O4, the following figure shows its molecular structure formula.
The following is also an experiment to show you the covering power of the pigment itself. Since the experimental steps of the covering power have been introduced before, I will not repeat them here.
Deep Alchemilla Red
Since it has been introduced alizarin red, it will then talk about deep alizarin red, although its name is deep alizarin red, but its color material is completely different from alizarin red, its color material belongs to the perylene-based PR179, its color phase is dark date red, with a high degree of transparency.
Its molecular formula is C26H14N2O4, and the molecular structure formula is as follows.
Its relative density is 1.41-1.65, average particle size is 0.07-0.08/μm, oil absorption is 17-50 (g/100g) also a low oil absorption pigment, its weather resistance is 5 stars, which is better than alizarin red.
Let's see its transparency by the following experiment.
This experiment is similar to the covering power experiment, except that what we need to observe later is the clarity of the black line under this paint coverage, the clearer it is, the better the color transparency.
Scarlet
Scarlet is also a red pigment of the perylene family, with a relative density in the range of 1.43-1.52, an average particle size of 0.15/μm and an oil absorption of 45-49(g/100g), which is also a low oil absorption pigment.
The drying time of the pigment itself is about 96±5 hours, and it is a fully transparent pigment with high light and weather fastness and good solvent resistance.
Its color phase is red, its molecular formula is C40H26N2O6, and its molecular structure formula is as follows.
由于它是一个全透明的颜色，在这里我们测试了一下它的透明度。如下图：
Permanent light red
Permanent light red, whose main pigment is PR112, is a single azo red pigment with high coloring strength and excellent light fastness, weather resistance of 4 stars, and a brilliant red color.
Its relative density is 1.38-1.65, the average particle size is 0.11/μm, and the oil absorption is 35-88(g/100g), which is a medium oil-absorbing oil pigment.
Of course, it should also be mentioned that its drying time is also around 96±5 hours, its transparency is translucent, its molecular formula is C24H16Cl3N3O2, and the molecular structure formula is as follows.
When it is added with different proportions of titanium white, its color changes.
Quinacridone Rose
Although these pigments have small molecular weight and simple molecular structure, they have excellent performance in heat resistance, light resistance and migration resistance, and they even perform well under low concentration and washout conditions, but the disadvantage is that the dispersion is slightly worse.
Rubens' quinacridone rose red is made of PV19 pigment, you may be confused when you see this pigment, it is obviously pigment violet, why is it classified as red pigment? This is because although pigment violet 19 is called pigment violet, it is not the kind of purple that is generally considered, but a beautiful peach color, so it is usually classified as a red pigment.
The same goes for a look at some of its basic pigment physical properties.
Its color phase is red light purple, it is β crystal type PV19, the relative density is 1.5-1.8, the average particle size is 0.05-0.1/μm, the oil absorption is 40-70(g/100g), it belongs to a low oil absorption pigment, the drying time of this pigment is also about 96±5 hours, it belongs to a full transparent pigment. The weathering resistance is five stars, with excellent light and heat resistance stability. Its molecular formula is C20H12N2O2, and its molecular structure formula is as follows.
A transparency test was also done here. The results are as follows.
In addition, we chose Brooks and Old Holland, using the same color 425 Rose Red and E29 Scheveningen Deep Rose Red, to do a coloring power comparison with our own quinhydrinone Rose Red, as follows.
Rubens B21 quinacridone rose red, Old Dutch E29 Scheveningen deep rose red, Brooks 425 rose red
The darker the color is, the stronger the coloring power and the higher the color saturation in the same amount of white.
Violet
Violet is also the color pigment of PV19, but it is not the same as quinacridone rose, it's is (γ crystal type) PV19, a blue light red pigment. Pigment violet 19 (γ crystal type) has a wide distribution of pigment particle size, which has a greater impact on the coloring performance. If the average particle size is smaller, its sunlight fastness and weathering fastness is worse, but the brighter the color light and the higher the coloring power, if the average particle size is smaller, the bluer the color light and the sunlight fastness and weathering fastness is better.
The drying time of violet pigment is slightly shorter, about 72±5 hours, it is a fully transparent color, with five-star weathering resistance and excellent sun fastness.
Also add different white pigments, you can see its color change.
Here too, Brooks and Old Dutch used the blue phase of PV19 of 423 magenta and E30 Scheveningen violet to do a control test with the following results.
Old Holland E30 Scheveningen Violet, Rubens C313 Violet, Brooks 433 Magenta
Scarlet
Crimson is a quinacridone red pigment with a yellowish hue, its alias is also called quinacridone big red, the hue is warm from the color card color, it is a fully transparent color system.
The drying time of this pigment is also about 96±5 hours, the relative density is 1.58, the bulk density is 13.1(lb/gal), the oil absorption is 38(g/100g), it is a low oil absorption pigment, the pigment property belongs to full transparency. Weather resistance five stars, with excellent light and weather fastness.
According to its own pigment properties here is also tested its transparency.
Magenta
Magenta pigment should be considered a relatively common red pigment, from the classification of the color pigment is also a quinacridone red pigment, the color phase with blue bias, a bright blue-red, its relative density is between 1.40 ~ 1.50, the average particle size 0.06 ~ 0.07/μm, oil absorption 40 ~ 65 (g/100g), belongs to the low oil absorption pigment.
The drying time of this pigment is also about 96±5 hours, and it belongs to a translucent pigment with five-star weather resistance, relatively excellent migration resistance and outstanding thermal stability. Its molecular formula is C22H16N2O2 and the molecular structure diagram is as follows.
下图为品红加入不同比例的钛白之后，原色和混色之后的不同色彩变化。
A control experiment was also done on the coloring power of 303 magenta pigment and D181 Old Dutch magenta using the same pigment as McHardin and Old Dutch, and the results were as follows.
Old Holland D181 Magenta, Rubens B213 Magenta, McHardin 303 Magenta
[Remark: Since the naming of each brand of pigment will be different, so the name is not the same, but the color material is the same, and none of the single color material hue will be too different. This is also a prerequisite for the control test.
(Note: The transparency of the pigment mentioned in the article is a physical property of the pigment material itself, and is not related to its thinness.
We are nearing the end of this article, so I would like to add a few more tips related to pigments in this issue.
Organic Pigments
This is because organic pigments generally have higher oil absorption than inorganic pigments, and pigments with high oil absorption, if the dry oil in them is not enough, it will lead to the oil not being able to cover the pigment, and the phenomenon of color flip will occur more easily.
In addition, the oil absorption is directly proportional to the oil absorption rate, so it is necessary to follow the principle of "fat cover thin" when using, that is, the oil absorption rate of the lower layer of pigment should be lower than that of the upper layer, otherwise the color layer will fall off later, which will affect the preservation value of the work.
After reading the article, we will also find a problem, that is, among the organic colors in this issue, there are several quinacridone, perylene and quinone pigments that are fully transparent or translucent, among which the transparent colors can replace the traditional transparent alizarin red for overdyeing.
When we introduced inorganic pigments, we mentioned that we can judge the quality of this pigment by its weight, and the same applies here, except that these organic colors are generally lighter, and if your pigment is too heavy, it is likely that some other fillers have been added.
