When you see a distinctively blue-tinted fuel at a depot, or a lubricant that carries a deep blue colour right out of the drum, there is a very good chance Blue 79 is responsible. Solvent Blue 79 (CAS No. 64553-79-3) is one of the most widely used blue petroleum dyes in the world — an anthraquinone-based colourant that was specifically engineered for exceptional solubility in fuels, oils, and organic solvents.
In this guide, we will cover everything you need to know about Blue 79: its chemistry and origins, why it replaced older blue dyes, where it is used today, and what to look for when sourcing it. If you are involved in fuel blending, lubricant manufacturing, or industrial dye procurement, this article is written with you in mind.
What Exactly Is Blue 79?
Blue 79, officially designated C.I. Solvent Blue 79, is a synthetic anthraquinone dye with the CAS number 64553-79-3. Its core chemical description is 9,10-anthracenedione, 1,4-diamino-, with N, N-mixed 2-ethylhexyl, methyl, and pentyl derivatives.
Here is the key backstory: Blue 79 was originally developed by BASF as a high-solubility form of Solvent Blue 35 (also known as Oil Blue 35 or 1,4-bis(butylamino)anthraquinone). The older Solvent Blue 35 works well as a blue colourant, but in powder form it dissolves only up to about 2% in xylene — far too low for efficient industrial use. By adding longer, branched alkyl side chains to the anthraquinone molecule, BASF created Blue 79, which can form stable liquid solutions at concentrations exceeding 60% solids in xylene, remaining stable even down to -20°C.
This dramatic improvement in solubility was a game-changer. It meant refineries could work with a ready-to-use liquid dye instead of handling hazardous powders — safer, faster, and far more consistent in application.
Key Chemical Properties of Blue 79 (CAS 64553-79-3)
The table below provides a quick-reference overview of the essential properties of Blue 79:
| Property | Details |
| C.I. Name | Solvent Blue 79 |
| CAS Number | 64553-79-3 |
| Chemical Class | Anthraquinone (1,4-diaminoanthraquinone derivative) |
| Base Chromophore | Same as Solvent Blue 35 |
| Hue | Reddish Blue |
| Solubility | Oil-soluble; >60% in xylene; fully miscible in fuels |
| Physical Form | Liquid (in solvent) |
| Common Solvents | High-flash (HF) solvents, Xylene (XY) |
| Recommended Dosage | 10–20 ppm in petroleum products |
| Shelf Life | ~2 years (stored at 5–40°C, sealed containers) |
| Key Advantage | Dramatically higher solubility vs. Solvent Blue 35 powder |
| Commercial Names | Sudan Blue 673 (BASF), Sudan Blue B, Automate Blue ER, Dyeguard Blue 79 |
These properties make Blue 79 the default choice for any petroleum or industrial application requiring a reliable, high-performance blue dye in liquid form.
Primary Applications of Blue 79
1. Fuel and Petroleum Colour-Coding
The dominant application for Blue 79 is colouring petroleum fuels. Refineries worldwide use it to colour-code specific fuel grades — distinguishing different octane levels of gasoline, various diesel sulphur grades, aviation fuels, kerosene, and gas oil. In some jurisdictions, blue-dyed diesel is specifically designated for governmental and institutional vehicles, making it easy to detect fuel theft or misuse.
Blue 79 is also a key ingredient in green fuel dye formulations. Because green is produced by combining a blue dye with a yellow dye (typically Solvent Yellow 107), Blue 79 is used alongside yellow dyes to achieve the precise green shade required by certain national fuel-marking regulations.
2. Lubricants, Hydraulic Fluids, and Industrial Oils
Transmission fluids, gear oils, hydraulic oils, and cutting fluids are often coloured blue for brand differentiation and product identification. Blue 79 provides a clean, vivid blue that remains stable over long storage periods and does not degrade under the thermal conditions typical of working machinery.
3. Wax, Candle, and Speciality Product Colouring
Blue 79 dissolves cleanly in paraffin and other wax systems, making it a reliable option for candle manufacturers who need a deep, consistent blue without sediment or wick-clogging issues.
4. Printing Inks and Coatings
In oil-based ink systems, Blue 79 delivers strong tinting strength and rapid dispersion. Its anthraquinone structure also provides inherently better lightfastness compared to azo-based dyes, which is an advantage for certain ink and coating applications exposed to sunlight.
Application Overview Table
| Application Sector | Specific Use | Why Blue 79 Is Preferred |
| Fuel & Petroleum | Gasoline, diesel, kerosene, aviation fuel | Exceptional solubility, consistent hue, liquid-to-liquid handling |
| Green Fuel Dyes | Mixed with Solvent Yellow 107 for green shades | Precise colour control, stable blend |
| Lubricants & Fluids | Transmission fluid, hydraulic oil, gear oil | Thermal stability, no residue, vivid colour |
| Wax & Candles | Paraffin, soy wax, gel wax colouring | Clean dissolution, no wick clogging |
| Printing Inks | Oil-based ink formulations | Strong tinting, good lightfastness |
Blue 79 vs. Other Common Blue Solvent Dyes
How does Blue 79 compare with other blue dyes used in the petroleum and industrial sectors? Here is a side-by-side look:
| Parameter | Blue 79 | Solvent Blue 35 | Solvent Blue 98 | Solvent Blue 97 |
| CAS Number | 64553-79-3 | 17354-14-2 | 74499-36-8 | 32724-62-2 |
| Chemical Class | Anthraquinone (alkylated) | Anthraquinone (base) | Anthraquinone | Anthraquinone |
| Physical Form | Liquid | Powder | Liquid | Powder |
| Solubility in Xylene | >60% | ~2% | High | Moderate |
| Primary Use | Fuel & oil colouring | Fuel, wax, inks, stains | Fuel & oil colouring | Plastics (PS, PET, PC, ABS) |
| Hue | Reddish blue | Blue | Blue | Greenish blue |
| Lightfastness | Good | Good | Good | Very good (7–8) |
| Handling Safety | Liquid — lower risk | Powder — dust hazard | Liquid — lower risk | Powder — dust hazard |
The core advantage of Blue 79 over the original Solvent Blue 35 comes down to practicality: the liquid form eliminates powder-handling hazards, ensures instant dispersion, and allows for far more accurate dosing in automated injection systems.
Case Study: Improving Fuel Depot Safety and Efficiency with Blue 79
Background: A national oil marketing company operating a network of fuel storage depots across the Middle East was experiencing recurring issues with their blue fuel dye programme. Their existing setup relied on Solvent Blue 35 in powder form, which required manual weighing and pre-dissolution in small batches of xylene before injection into fuel storage tanks. The process was slow, generated significant dye dust exposure for workers, and produced inconsistent colour from batch to batch.
The Problem: Depot workers were raising health and safety concerns about repeated exposure to powdered anthraquinone dye dust. Quality audits revealed that colour intensity varied by up to 35% between tanks that had been dyed using the powder process, and three batches in a single quarter had been rejected for insufficient blue tinting.
The Solution: The company transitioned to a pre-formulated Solvent Blue 79 (CAS 64553-79-3) liquid concentrate supplied in high-flash solvent base. The liquid was delivered in sealed drums, eliminating all powder handling. It was injected directly into the fuel flow using the existing proportional dosing systems at each depot, calibrated to deliver 15 ppm of Blue 79.
Results:
| Metric | Before (Blue 35 Powder) | After (Blue 79 Liquid) |
| Colour Consistency | ±35% variation | ±4% variation |
| Batch Rejection Rate | ~8% per quarter | 0% (12 months post-switch) |
| Worker Dust Exposure Incidents | 6 per year | 0 |
| Dye Dissolution Time | 45–60 min per batch | Instant (pre-dissolved) |
| Annual Dye Handling Cost | Baseline | ~22% reduction |
| HSE Audit Findings (Dye-Related) | 3 in 12 months | 0 in 12 months |
Key Takeaway: The switch from powdered Solvent Blue 35 to liquid Blue 79 did not just improve colour consistency — it fundamentally improved workplace safety and operational efficiency. This is exactly the kind of gain that the shift from powder to liquid petroleum dyes was designed to achieve, and it is why Blue 79 has become the industry standard for blue fuel colouring.
What to Look for When Sourcing Blue 79
Because Blue 79 is a mixture of alkylated anthraquinone derivatives (not a single pure compound), product quality and performance can vary between manufacturers. Here are the criteria that matter most:
Zero insolubles: The liquid dye should be completely free of undissolved particles. Even trace insolubles can accumulate in fuel injection lines, dosing pumps, and storage tank filters.
Full miscibility: Blue 79 must dissolve instantly and completely in the target fuel or oil, producing a clear, homogeneous blue with no haziness.
Colour strength consistency: Batch-to-batch colour strength should be verified spectrophotometrically. A reliable manufacturer will provide a certificate of analysis confirming dye content and colour strength for every production batch.
Low-temperature stability: The liquid formulation should remain clear and stable at temperatures down to at least -20°C, without crystallisation or phase separation.
ISO certification: Look for manufacturers with ISO 9001:2015, ISO 14001:2015, and ISO 45001:2018 certifications as evidence of quality, environmental, and safety management.
Anar Chemicals LLP (anarchem.com) manufactures Blue 79 in both high-flash and xylene solvent bases, backed by over four decades of experience in dyes and speciality chemicals. They are an ISO 9001:2015, ISO 14001:2015 & ISO 45001:2018 certified facility, supplying petroleum dye solutions to refineries and fuel companies globally. You can explore their complete Liquid Petroleum or Fuel Dyes range on their website.
Frequently Asked Questions About Blue 79
Q: What is Blue 79 used for?
Blue 79 (Solvent Blue 79, CAS 64553-79-3) is primarily used for colouring petroleum fuels, lubricants, and industrial oils to enable visual identification and grade differentiation. It is also used in wax, candle, and ink formulations that require a stable blue hue in non-aqueous systems.
Q: What is the CAS number for Blue 79?
Solvent Blue 79 is listed under CAS number 64553-79-3. This is the standard CAS registration for the alkylated 1,4-diaminoanthraquinone derivative used in petroleum dye formulations.
Q: How is Blue 79 different from Solvent Blue 35?
Blue 79 is the high-solubility, alkylated form of Solvent Blue 35. Both share the same anthraquinone chromophore and produce similar blue hues, but Blue 79 has longer alkyl side chains that dramatically improve its solubility in fuels and organic solvents. Solvent Blue 35 in powder form dissolves only up to about 2% in xylene, while Blue 79 can form stable solutions at concentrations above 60%.
Q: What is the typical dosage for Blue 79 in fuel?
Blue 79 is typically used at 10 to 20 ppm in petroleum products, though the exact dosage depends on the target shade intensity and the specific fuel or oil being coloured.
Q: Does Blue 79 affect fuel performance?
No. Solvent Blue 79 is chemically inert in hydrocarbon systems at the concentrations used. It does not alter combustion characteristics, octane or cetane ratings, or engine performance.
Q: Why do refineries use blue fuel dyes?
Blue fuel dyes serve multiple purposes: differentiating fuel grades during storage and transport, identifying governmental or institutional-use fuel to prevent theft, and meeting country-specific regulatory requirements for fuel colour-coding.
Q: Where can I buy high-quality Blue 79?
Blue 79 is available from speciality petroleum dye manufacturers such as Anar Chemicals LLP (anarchem.com), an ISO 9001:2015, ISO 14001:2015 & ISO 45001:2018 certified company with over 40 years of experience. They produce Blue 79 in both high-flash and xylene solvent bases.
Q: How should Blue 79 be stored?
Store in tightly sealed containers, away from direct sunlight, at temperatures between 5°C and 40°C. Under proper conditions, the shelf life is approximately 2 years from the date of manufacture.