Natural inorganic pigments

Natural inorganic pigments are among the oldest used by humans. They first appear in the funeral preparation of human remains from 60,000 years ago, and in polychrome cave art from about 20,000 years ago. Mined in prehistory from surface deposits of clay and rock, many inorganic pigments have shown extraordinary permanence over long periods of time.

With few exceptions, inorganic pigments are combinations of a mineral element with oxygen and other elements (most often sulfur, silicon or carbon) that fall in the chemical classes known as oxides, oxide hydroxides, sulfides, sulfates, silicates and carbonates.

The pigments in this category that have been of importance to watercolor painting include:

Red earths. A large and diverse category of pigments, all made from earths (mostly clays) containing large proportions of iron oxide (the dark violet to light red hematite or everyday rust, the orange to yellow lepidocrocite, or the dark brown maghemite) that is processed and sold as natural iron oxide. The pigment color may range from a dull yellow through a dull deep yellow, dull orange, dull red or dark brown (listed either as PR102 or PBr7) to near black (PBr6). The color depends on the average particle size, the presence of manganese or other elements (which darkens and dulls the color), and whether water is chemically bonded within the iron oxide crystals. (The dull red orange to yellow hydrous oxides contain water, the maroon to dull red anhydrous oxides do not.) Although red iron oxides occur in all parts of the world and have been used as pigments since antiquity, rich deposits are currently found near Malaga, Spain (Spanish red, which has a characteristic brownish undertone) and in Ormuz, in the Persian Gulf (Persian red). Historically, European sources of yellow brown earths were mined near Leghorn or Siena (in Tuscany, Italy); these are the siennas, containing roughly 50% iron oxide and less than 1% manganese dioxide. The dark red or brown earths or umbers, containing 45%-70% iron oxide and 5% to 20% manganese dioxide, were originally imported to Europe from Turkey (via Venice), but are now mined primarily in Cyprus. (The name probably derives not from the Italian region of Umbria but from the Latin ombra or shadow, referring to the original use of dark iron oxides as shadow colors.) These earths are often “burned” (calcinated or roasted at a dull red heat) to darken them (burnt sienna, burnt umber), a technique that was probably suggested around 2000 BCE by the visible reddening or darkening of pottery after it had been fired or glazed. And natural manganese ores have sometimes been added to red earths create darker red, violet or black colors in pottery clays or glazes. (Due to growing scarcity of high quality natural deposits of iron oxides, most artists’ colors are now made from synthetic iron oxides, for example the same pigments manufactured for wood stains.)

Yellow earths. Natural earths containing silica and clay, hydrous forms of iron oxide (yellow brown limonite or the brown yellow to green yellow goethite), and traces of gypsum or manganese carbonate. Like the red iron oxides, they are found around the world and have been used as pigments since prehistory. French ochre, historically one of the best grades of limonite, contains about 20% iron oxide and is high in silica. Currently workable deposits for yellow oxides are located in the Republic of South Africa and France. Most often sold as yellow ochre (PY43) or brown ochre. Most yellow clays are normally not “burnt” as heat does relatively little to alter their color.

Green earths. Clays containing large amounts of silica and the green minerals glauconite and celadonite, consisting essentially of hydrous iron, magnesium, and aluminum potassium silicates. Color varies from a dark, grayish blue green to a dark, dull yellowish green. Completely lightfast and chemically inert, green earth or terre verte has been used around the world since ancient times. In Europe, the first documented use in paintings is in Roman frescos; it was also commonly used in the Middle Ages as an underpainting for flesh tones and shadows. Originally extracted from deposits in central Europe (today’s Czech Republic), near Verona (Italy), or in France, modern supplies come from high quality deposits in Cyprus. Most of these pigment deposits originated as marine clays. In watercolors the typical color is light valued (diluted), and paints made from the genuine pigment tend to be thin and gummy. The label terre verte is often applied to paints mixed from other inorganic pigments, typically chromium oxide green (PG17) or viridian (PG18) mixed with a red iron oxide. (See also the section on chromium compounds.)

This article comes from handprint edit released

Features of Cobalt Blue Pigment

Cobalt blue is a very important inorganic blue pigment, it has very wide applications. What’s the main feature of Cobalt Blue Pigment? Let us analyze this.

Cobalt blue pigment, also called pigment blue 28, it mainly composited by Cobalt Aluminate(CoAl2O4). According to its chemical formula, the content of Alumina oxide should be 57.63%, cobalt oxide is 42.36%.But in Cobalt blue pigment, Alumina oxide is contained about 65% to 70%, Cobalt oxide is 30% to 35%.

(Cobalt blue pigment from Nolifrit:)


Cobalt blue belongs to spinel group, it’s cubic with spinel crystal. Cobalt blue Density ratio is 3.8~4.54g/㎝3, Covering power is 75~80g/㎝2, Oil absorption 31%~37%, Bulkiness 630~740g/L.

Cobalt blue has very bright color. it’s highly weather-proof, alkali resistant, which can bear varies of solvent and its heat resistance can be 1280℃. Cobalt blue is also a environmental friendly and nontoxic high temperature resistant inorganic pigment.

Cobalt blue pigment is mainly applied to heat resistant paint, ceramic, enamel and glass. Coloring for heat resistant industrial plastic. And it can be also the pigment for art, in this field, Cobalt blue pigment is much expensive than other inorganic pigment.

(Enamel cookware in Cobalt blue color:)


According to the above description, let us sum up main features of Cobalt blue pigment:

Name Compositions Heat Resistance Corrosion Resistance Price Applications
Cobalt Blue CoAl2O4 1280℃ Nice Contact us to know its price Heat resistant paint, ceramic, enamel and glass

Hunan Noli Enamel Co,. Ltd is the leader manufacturer of Cobalt Blue pigment in China, Focusing on the production of Cobalt blue pigment over 30 years.

It can be widely applied in enamel coloring, and its heat-resistance can be more than 1280℃, which is approved and welcomed by most of our customers.

Heat Resistance of Cadmium Yellow Pigment

Cadmium Yellow, also called Pigment Yellow 37, is a high-performance inorganic yellow pigment. Cadmium Yellow has very bright color and strong coloring power, Stable light fastness. And it’s weather-proof, heat resistant, with no bleeding and transference. Its heat-resistance better than Chrome Yellow, of course much better than Benzidine Yellow and all of other organic pigments.

Well, How’s the Heat Resistance of Cadmium Yellow Pigment?

Pure Cadmium Yellow is a solid solution composited by Cadmium Sulfide and Zinc Sulfide. Cadmium Sulfide has two stable forms in normal temperature:

One is β—CdS, it’s cubic crystalloid; The other one is α—CdS, it’s Hexagonal crystalloid. The former one is stable in low temperature, heat-resistance is less than 500℃; The latter one is stable in high temperature, melting point: 1405℃, heat-resistance is higher than 600℃. In normal temperature to 500℃, the two crystalloids can maintain stable coexistence.

(Enamel cookware in Cadmium Yellow color:)20180811033150_59303

High temperature resistant Cadmium Yellow’s heat-resistance is depend on the ratio of cubic crystalloid β—CdS and Hexagonal crystalloid α—CdS. The more hexagonal crystalloid α—CdS contains in Cadmium Yellow, the higher its heat-resistance will be.

Hunan Noli Enamel Co,. Ltd is the leader manufacturer of Cadmium Yellow pigment in China, Focusing on the production of Cadmium pigment over 30 years.

It can be widely applied in enamel coloring, and its heat-resistance can be more than 800℃, which is approved and welcomed by most of our customers.

(Cadmium Yellow pigment from Nolifrit:)


Porcelain Enamel Cups: What A Nice Choice in Hot Summer

Summer is usually hot, you will sweat even you do not get moved. It’s quite necessary to drink water after you sweated a lot. Then a healthy and beautify cup is a must. There are many kinds of cup in the market to choose from. For example, Glass cup, enamel cup, ceramic cup, plastic cup, stainless steel cup, etc…How to choose, is there anything need to care about?

Generally, consumers may not know which kind of material for cup is most reliable. Here we can say, glass one should be one of the best choice. Why?  Because glass contain no organic chemical material, and its surface is very smooth, easy to clean, bacteria and virus won’t survive in the glass inner wall. But glass is of high thermal conductivity, so when using a glass cup, it’s quite easy to be scalded. And it’s easily be broken when pour hot water into a glass cup.

And the colors of glass cup is very few to choose from, it has no ornamental value at all. This make us always ignore them. Do we have any other choice? Of course, that must be the enamel cup.

Enamel cup is coated with vitreous porcelain enamel. The enamel frit is milled to enamel powder and after almost 1000℃ firing, it can adhere to Its steel body. After cooling, the surface can be very smooth, it’s without any toxic material. Except for all the advantages a glass cup have. It can be also colored by inorganic pigment and decorated by enamel deco, which makes it colorful and good looking. If you own one of the follow enamel cup, will you drink more water than ever before?

Porcelain Enamel Cups

Some one would prefer plastic cup, but plastic cup should be the worst choice. As it may contain many toxic chemical material. And it can even release toxic material to the water when it filled with hot boiling water. Especially when it filled with strong acid or strong alkaline beverages, the toxic heavy metal like Pb, Hg will be dissolved to the liquid. So when using a plastic cup, you must choose the cup meet with the health standard.

Anyway, a cup with porcelain enamel coating can be the best choice for you to drink.

Porcelain Enamel Coating

From world-class raw materials and production facilities to global presence and process knowledge, we develop product solutions for your porcelain enamel coating and frit needs. Through technical know-how, we formulate specialty frit based products that meet the needs of the consumer white goods, hot water tanks, sanitary ware, cookware, and other industries. We have dedicated R&D centers and staff specialists to assist customers in achieving consistent, high quality output and increasing productivity. As an industry leader, we specialize in understanding the role of porcelain enamel coating and glass enamels across a wide spectrum of applications.

Frits are the basis and main component of an porcelain enamel coating. Each PEMCO® frit is individually designed to address the complex variables of chemistry and end use application. Quality raw materials are blended and melted to create a frit technically adapted for different applications. Our range of products is composed of ground coat, transparent, opaque and white frits that are engineered to match desired color, aspect, or effect.

We engineer PEMCO® frits into a pre-milled, ready-to-use formulation to provide customers with a powder for liquid application. The use of pre-milled products eliminates the need for costly milling equipment. Just add water and mix! One of the most successful innovations in the porcelain enamel coating industry has been the development and continued improvement of our portfolio of PEMCO® Electrostatic Powders. The advantages of electrostatic powders include automated application, elimination of hazardous waste, reduction of energy costs for milling and drying and labor costs in mill room and set up, excellent finish quality, and maximized utilization of material.

This article comes from princecorp edit released

Nolifrit Anti Fishscale frit for Enamel Coating

The fishscale defect in the enamel coating on steel products is well known as an undesired phenomenon. The fishscale defect is caused by hydrogen gas pressure at the enamel-steel interface that causes the enamel to fracture. This problem limits enamellers to low carbon steel in order to avoid fishscale defects. The customers of frit producers often send many different types if steel and ask “is it possible to enamel such type of steel?” This demand has become critical as the hot water tank industry has grown. Consequently, this fact has required a solution for high carbon steel to be found.

Fishscale is a well-known defect in the porcelain enamel industry. Enamellers strictly control their steel to be defect free so they choose special quality steel. When the steel batch arrives, enamellers take samples from each steel coil and carry out initial tests for fishscale. Even with all these precautions, enamellers still face fishscale sometimes. This is mainly caused by variation with the steel coil. It has been seen that development of fishscale resistant enamel could work at least as an insurance mechanism but also could le t enamellers to use lower quality steels.

Fishscale is mainly caused by hydrogen itself. In practice, hydrogen is everywhere in the enameling operation. The main source of hydrogen is moisture in the air. The H2O penetrates the enamel and separates into oxygen and hydrogen. Oxygen is consumed in the adherence reaction, and atomic hydrogen diffuses inside the steel. Atomic hydrogen is too small to penetrate into the steel. hydrogen re-combine to form H2 gas. When the temperature is raised, the hydrogen solubility of steel also increases. This means that steel can absorb more H2 than its capacity. During cooling, hydrogen gas tends to go out from steel due to decreased solubility hydrogen release causes fishscale defects on the enamel surface. The intensity of fishscalling is directly linked with amount of water in the sys tem as well as the absorption capacity of steel.

In the enameling industry, cold rolled steel Is used with several specifications well known by steel producer. Many steel producer have enamel quality steel in their product line. The main requirement is the production method should be cold rolling and the carbon content of steel should be as low as  possible. Several works have been carried out to overcome fishscale.

The fishscale phenomena is affected by both steel and enamel properties. It has been found that adding nickel addition to the enamel helps decrease fishscale. In the work, different enamel systems have been developed for different applications. The steel has 0.25% carbon content, and the result was proved with side by side application.

The main measures to avoid fishscale on enamel coating:

  1. The choice of steel plate: Enamel steel is always the best choice, then cold rolled steel, hot rolled steel is most likely to have fishscale.
  2. The surface treatment of steel plate: Try not use acid pickling, or use little acid pickling in very short time and use corrosion inhibitor when acid pickling.
  3. For the ground coat: Choose the ground coat with suitable adherence.
  4. For the milling additives: Use quartz, carbonate and quality clay in suitable amount.
  5. For the firing process: Fire in reasonable temperature and time, make sure not to burn.
  6. For the thick steel plate, only accept coating on single face.

Hunan Noli Enamel Co.,Ltd has developed a Anti fishscale porcelain enamel frit 2466 to avoid the fishscale defect. It can be even applied in hot rolled steel and the effect can be acceptable.

Enamel coating mixed with 2466 : (Nolifrit)


Enamel coating with normal enamel frit:


Nolifrit Enamel Frit Exported to Central America

Since the arrival of May, the enamel industry has entered its hot season, and we have received orders for enamel frit from customers in Central America. In recent years, Nolifrit has taken the initiative to develop the international market, actively responding to the “One Belt and One Road” policy, and striving to adapt to the new normal of economic development. The effect of market expansion is gradually emerging. In the past few days, Nolifrit has been working hard to promote production, and all employees have worked hard to ensure the timely delivery. The factory has shown a good situation of both production and sales.QQ图片20190511105942_副本

Coming into the Nolifrit production workshop, one and another converter furnaces is rotating at a constant speed, and the molten enamel frit is then quenched.”This year’s situation is quite well, the current orders has been scheduled to June. In order to catch orders, all of our employees are on duty, and now we are still hiring new employees.” When it comes to the sales situation, the head of the company’s administrative department speaks with proud.QQ图片20190511105954_副本

This batch of enamel frit produced for Central American customers can be delivered on schedule, which is the result of the joint efforts of Nolifrit employees. In order to complete the production tasks with quality and quantity, the company’s leadership is reasonably dispatched and production arranged orderly; the supply department closely tracks and strictly guarantees the timely storage of raw materials; the leaders of the production department are willing to work hard and dedicate. All current production tasks are being carried out orderly. The main products of Nolifrit include nearly 2,000 kinds of enamel ground coat, cover coat, transparent frit, and vitreous enamel powder, inorganic pigment, etc. They are exported to foreign markets, such as Southeast Asia, Middle East, Europe and the United States. The continuous overseas orders fully demonstrates the customer’s acceptance of Nolifrit quality.QQ图片20190511110004_副本

Looking at the container trucks loaded with various enamel frits drive out of factory, the hearts of the Nolifrit people are full of pride. “Let Nolifrit go global” is our unshakable goal. Twenty-three years of history is just like a wave, and now we are developing step by step. We will continue to serve global enamel users with our professional service, excellent work enthusiasm and technical and R&D advantages accumulated for over the past 20 years.

Nolifrit Solution for Black Dots on Cover Coat

Black dots(bubbles or pinholes) on cover coat (mostly on white cover coat) is a common fault of enamel coating process. It may happend in many areas like enamel cookware or enamel panels. What’s the main reason of this fault? And how to avoid this? With experience for over 30 years, technical team from Nolifrit is very professional to solve all kinds of problem like this, and we even have successful cases before:

Typical Case:

One of top 10 manufacturers of cookware in the Middle East.


Black dots on white cover coat (for enamel saucer)

Main Causes:

1, The steel substrate is not clean enough.

2, There are too much C, S, P contained in steel substrate.

3, There are impurities mixed in cover coat enamel slurry.

4, Fire temperature is not reasonably controlled, so the ground coat is rare fired.

Nolifrit Solution:

1, Before enameling, the steel plate should be cleaned, without any rust or dust.

2, Choose better steel plate, enamel grade steel is highly recommended.

3, Avoid the pollution of enamel slurry, and take more careful on the use amount of clay and other additives.

4, Reasonably control the temperature of furnace, ground coat should be fully fired.

(Those advises are all based on our customer’s situation, which subject to the actual practice.)


Problem solved after customer take our advices:20190127012903_62344_副本_副本Hunan Noli Enamel Co,. Ltd is the leader manufacturer of porcelain enamel frit and enamel powder in China. Focused on enamel coating for over 30 years.

We can offer very professional technical guidance and product solutions. To solve the problems our customers will likely face in their production. We have successfully solved most of the problem of our customers, which makes us with very good reputation and build up the profound trust with our customers.

What is porcelain enamel?

In general terms, vitreous enamel, porcelain enamel, copper enamel and jewelry enamel all refer to the same thing. Enamel is a glassy compound applied to and bonded by heat (fusion) to a metal surface; to a copper surface at 1450 degrees F., and to a glass surface at 1100 degrees F. to 1500 degrees F.

The most common glass is a fusion of silica, soda, lime, and a small amount of borax. Though normally transparent, various amounts of opacity can be produced by adding or growing crystals within the glass structure. A wide range of colors are produced by incorporating certain elements, mostly transition metals.

The physical properties of glass can be controlled to permit bonding to most metals, for example, gold, platinum, silver, copper, steel, cast iron and titanium.

The word ‘Porcelain Enamel’ refers to the glass material as well as to the finished product.

This article comes from facebook website edit released

Nolifrit Brief Analysis on Viscosity of Enamel

Viscosity is a measure of the resistance of a liquid to flow. The greater the viscosity, the smaller the fluidity, and the unit of viscosity is Pa•s.

Enamel frit is similar to glass and has no constant melting point. The solid enamel layer is gradually softened and converted into a melt under the condition of constant heating. Therefore, the viscosity of the enamel is continuously changed, and there is no numerical mutation. This is different from crystals. When the crystal is heated to the melting temperature, its viscosity changes abruptly.

Nolifrit Brief Analysis on Viscosity of Enamel

In the first stage of enamelware firing, enamel powder layer decreases in viscosity with increasing temperature; in the later stage of firing, the enamelware gradually cools and the viscosity increases with decreasing temperature. When the viscosity reaches or exceeds 1012 Pa•s, the molten enamel layer becomes a solid enamel layer.

At a typical firing temperature, the enamel melt has a viscosity of 200 to 400 Pa•s.

The viscosity of the enamel depends mainly on the chemical composition of the enamel. The influence of the composition of the enamel on the viscosity is very complicated. The composition and content of the oxide are different, and the influence on the viscosity of the enamel is different in different temperature ranges.

Enamel frit manufacturer found that the introduction of monovalent alkali metal oxides, B2O3 and fluoride in the enamel can reduce the viscosity of the enamel melt; the introduction of SiO2, Al2O3, CaO, MgO, etc., makes the viscosity of the enamel melt increase. When the content of TiO2 in the formulation does not exceed 8%, the viscosity of the enamel melt is lowered; when the content exceeds 8%, the viscosity of the enamel melt is increased.

Milling additives like quartz, zirconium silicate, feldspar, titanium oxide, tin oxide, clay, etc., can not be completely dissolved in the enamel in short firing time and at lower temperature, so this makes viscosity of enamel melt improved.

The enamel with high viscosity is not conducive to the escape of gas in the enamel layer during firing, which increases the pores and bubbles of the enamel layer, and is not conducive to the flow of the enamel melt during firing, which tends to cause the fineness and gloss of the enamel surface to decrease. For enamel products requiring high-temperature firing, enamel with high viscosity is beneficial to improve the burning resistance and firing range of enamel products.