Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D1209-05 – Standard Test Method Technical Guide
Test Method D1209, often synonymous with APHA Color or the Hazen scale, provides a visual measurement procedure for assessing the color of clear, light-colored liquids. Developed to standardize the qualitative term “water-white,” it is critical for quality control in the paint, varnish, and solvent industries. This method compares the sample to standard Platinum-Cobalt solutions.
📐 Scope and Applicability
This test method is primarily applicable to materials where the color-producing bodies present have light absorption characteristics nearly identical to the platinum-cobalt standards. It is specifically designed for essentially light colored liquids. For darker liquids, such as soluble nitrocellulose base solutions, refer to Guide D365. Values are expressed in SI units per Clause 1.2, and test results must be rounded off to the nearest unit in accordance with Practice E29 for conformance determination.
| 📏 Referenced Standard | ⚡ Purpose / Application |
|---|---|
| ASTM D156 | Saybolt Color of Petroleum Products (Chromometer Method) |
| ASTM D365 | Procedure for darker liquids (Soluble Nitrocellulose Base Solutions) |
| ASTM E29 | Standard Practice for Rounding Off Test Data to Determine Conformance |
| ASTM D1193 | Specification for Reagent Water for Standard Preparation |
⚠️ Safety Compliance: This standard mandates the user to establish appropriate safety, health, and environmental practices. Specific hazard statements are located in Section 6 of the full standard. Consult the relevant Material Safety Data Sheet (MSDS) prior to handling samples.
⚙️ Significance and Historical Context
The property of color in a solvent varies significantly with its intended application. Before the formalization of the Pt-Co scale in 1952, the term “water-white” was loosely used to describe solvent color. Recognizing the need for a precise analytical benchmark, D1209 (similar to the APHA method described in Standard Methods for the Examination of Water and Wastewater) established a quantitative scale. This scale, originally defined by A. Hazen, utilizes specific concentrations of potassium chloroplatinate (K₂PtCl₆) and cobalt chloride (CoCl₂) to create a range of color standards from 0 (water-white) to 500.
💡 Technical Insight: The Platinum-Cobalt scale is integral to quality control. A solvent’s color directly indicates the degree of refinement or the cleanliness of the shipping/storage vessel. Even minor color deviations can affect the final tint and clarity of clear coatings and lacquers.
📊 Key Measured Properties and Scale Interpretation
The primary property measured is the color intensity compared against the Platinum-Cobalt (Pt-Co) standards. Materials are visually matched against these standards in matched Nessler tubes. The result is reported directly in Pt-Co units (or APHA units).
| 🎯 Pt-Co Unit Range | 🟦 Visual Characteristic | 📐 Typical Application |
|---|---|---|
| 0 – 10 | Water white | High purity solvents, ethylene glycols |
| 10 – 50 | Slight yellow tint | Commercial alcohols, diluents |
| 50 – 100 | Pale yellow | Low color lacquer bases |
| 100 – 250 | Medium yellow | Some processed oils, base materials |
| Up to 500 | Dark yellow / brownish | Maximum range for Pt-Co; darker liquids use D365 guide |
❓ Frequently Asked Questions
🔍 What is the difference between APHA Color, Pt-Co, and Hazen Scale?
These three terms are synonymous. The standard ASTM D1209 method is identical to the APHA (American Public Health Association) color method for water, and the unit is often referred to as the Hazen scale after its original developer, A. Hazen.
💡 What is the acceptable range for “Water White” on the Pt-Co Scale?
Technically, 0 is perfectly water-white. In industry practice, liquids with a Pt-Co color of 10 or less are often described as water-white. The standard uses matched Nessler tubes to visually determine the exact value down to the specific standard.
⚡ Does this standard apply to darker colored liquids?
No. D1209 explicitly states it is for “essentially light colored liquids.” For darker liquids where the color-producing bodies do not match the Pt-Co light absorption characteristics, the standard refers users to Guide D365, specifically for soluble nitrocellulose base solutions, or to the Saybolt Chromometer Method (D156) for petroleum products.
📌 How are test results rounded to determine conformance with specifications?
According to Section 1.2 of the standard, test results must be rounded “to the nearest unit” in the last right-hand digit used in expressing the specification limit. This must be done in accordance with the rounding-off method outlined in Practice E29.