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Clear liquid purity is measured using the APHA color scale and is essential for ensuring product safety and consistency and many various industries. Image Source: Flickr user Nathan Forget

Purity is an important factor imperative in the foods we eat, the medicines we take, and the water we drink. However, visual analysis of clear liquid color measurement is highly subjective, leaving a high margin of error in purity analysis. Color measurement using the APHA color index allows these various industries to maintain safety and consistency in their products.

Transparent plastic preforms are essential for companies that manufacture goods like beverages, edible oils, and intermediate chemicals like alcohols and glycols to form the container for the end product. The color of these preforms is equally vital, helping determine the final product's appearance and its impact on consumers' acceptance, buying decisions, and perceptions of quality.

Beyond influencing your customers, color consistency keeps manufacturing costs under control, since alterations can lead to waste. All cement the importance of color measurement at every stage of production to uphold quality assurance (QA) throughout the supply chain, from raw materials to finished goods.

The Challenges With Color Consistency in Transparent Plastic Preforms

Multiple factors can impact the appearance of transparent plastic preforms, from raw material variations to processing conditions and physical characteristics. All present specific challenges to overcome to achieve consistency and the desired appearance.

Variability in Raw Materials

Variability in raw materials is a frequent challenge for every plastics manufacturer, as well as producers who rely on plastic preforms.

Global regulatory bodies and consumers are embracing sustainability, leading to higher demand for the inclusion of more recycled polyethylene terephthalate (rPET). With this rising expectation comes new challenges, since rPET often contains high amounts of optical brightening agents (OBAs) to overcome yellowing. Every delivery of raw materials typically differs in that composition, making color measurement crucial to managing rPET variations successfully. Quantifying color at this stage empowers scientific, objective, and data-driven decisions to uphold aesthetics, quality, and performance.

Other challenges include variations in the amount and type of additives and pigments that can influence the final color. Additionally, contaminants like dust or residual color from previous runs may lead to alterations in appearance or clarity.

Physical Preform Properties

Transparent plastic preforms naturally present measurement challenges due to their physical properties.

Preform shapes and specifications represent the first difficulty. Contoured surfaces and variations in thickness inherently impact cooling rates, which can lead to alterations in color consistency. Inaccurate sample presentation can further influence measurement accuracy.

Additionally, transparent plastic preforms are susceptible to haze that affects color perception. This cloudy appearance is often caused by microparticles embedded within the plastic, which causes light to scatter when it interacts with the sample.

How Spectrophotometry Addresses the Challenges

Spectrophotometry is the most accurate and objective way to quantify color in transparent plastic preforms. Top-rated spectrophotometers solve the issues of manual visual evaluations — observer fatigue, error-prone assessments, and variabilities in surroundings that can affect how we perceive appearance.

Specialized Design for Transparent, Contoured Surfaces

This equipment provides scientific, numerical color data through specialized optical geometries and controlled lighting by measuring transmittance — the intensity of light at specific wavelengths within the visible spectrum that passes through the sample. Operators can then compare the readouts against established scales and indices, such as the Yellowness Index, to ensure the preform falls within acceptable tolerances, promoting consistent and repeatable results.

Higher rPET Content Without Guesswork

Tight color control with spectrophotometry is also how brands increase rPET without sacrificing appearance. When you have objective color data within seconds, you can raise recycled content while protecting appearance. Capture color measurement during incoming to set OBA dosing from data, not estimates. Using the same approach for in-process assessment and final inspection also helps identify alterations faster to uphold your quality control (QC) and support color consistency, even across different sites and suppliers.

In beverage packaging, color goes beyond appearance, it’s an unspoken promise of quality and consistency. For one global bottling company, color variation in PET preforms and plastic caps was becoming a costly risk. A shift in shade could erode brand trust, slow production, or trigger costly rework.

That’s when they turned to HunterLab.

Struggling with color variation across sites? Request a HunterLab demo and take control of your packaging color.

Why Color Consistency is a Bottler’s Business Advantage

• Brand Integrity: Consumers recognize visual differences—even minor inconsistencies in color can influence perception and purchasing behavior.
• Process Confidence: Consistent color signals stability in formulation, additives, and processing.
• Operational Efficiency: Catching out-of-spec color in real-time prevents rework, scrap, and costly downtime.

Functional additives like oxygen scavengers further complicated color control. The challenge was clear: measure preforms and caps with accuracy, no matter the size, material, or additive load.

Customer Challenge: Varying Tools, Oversized Preforms, and Manual Workflows

This global bottler operated across multiple plants, each using different tools:

• Most relied on ColorFlex EZ for caps
• Some sites used Vista® for beverage color, with limited preform measurement

Please note: ColorFlex EZ is no longer in production. Meet the upgraded ColorFlex L2, the industry's most advanced color spectrophotometer.

But the brand’s large-format PET preforms didn’t fit standard holders, compromising measurement consistency. Additive effects on color weren’t clearly quantified, and operators selected workspaces manually, increasing variability.

⚠️ Operational Risk: Inconsistent color across production lines can mean inconsistent quality on store shelves.

Moisture can change the color of fabrics in deliberate, overt ways or create subtle color shifts nearly imperceptible to the human eye. Image Source: Pexels user snapwiresnaps.tumblr.com

The Unseen Emporium in London, England is more of a laboratory than a design house. Through a daring and innovative combination of fashion, chemistry, and digital technologies, the three masterminds behind the label work to produce dynamic clothing, accessories, and lifestyle goods that respond to their environments based on specific stimulants.1 Among their most eye-catching creations are extravagantly tailored leather jackets that change color as the humidity in the room fluctuates, the moisture level creating vivid chromatic shifts. The phenomenon of hydrochromism—color change in response to water—has heretofore primarily been intentionally implemented in the textile industry as a novelty in the form of color-changing umbrellas and swimwear. The Unseen Emporium, however, is bringing it to a new level of artistry.

But hydrochromic textiles are not a recent invention. Although deliberately moisture-sensitive dyes with dramatic color changes may be in their infancy, some level of hydrochromism is inherent to most textiles already in use today, often to the consternation of textile manufacturers.

Dark cotton fabrics will display a greater degree of color change in the presence of moisture. Image Source: Pexels user snapwiresnaps.tumblr.com

New polymer products continue to flood the market, and there seems to be no end to the continued growth in plastic manufacturing. In 2024, the global molded plastics market reached a value of $541.2 million. Experts predict a compound annual growth rate of 7.5% over the next decade, which means the market's value will surge to over $1 billion by 2034. In this booming market, competition with large manufacturers may seem daunting, yet small business continues to thrive.

To stay competitive among these giants, choosing the right spectrophotometer for plastics is often the difference in product efficiency and quality. Understanding the value of color measurement in plastic production is the first step toward optimizing growth and increasing sales overall.

Utilizing Spectrophotometric Instrumentation in Plastic Production

Modern spectrophotometers measure more than the tristimulus values captured by basic equipment. They offer spectral measurement capabilities and can quantify appearance by considering the influences of gloss and texture on perception. This technology makes them an ideal choice for many plastics, which often feature various shapes, textures, and opacities.

Sample types determine the right measurement techniques for accurate color data, so understanding these characteristics that drive your approach is the first step to utilizing your color measurement solutions. For example, accurate color quantification for transparent plastic preforms requires measuring via transmission, while opaque plastics require reflectance measurements.

The device’s geometry is also critical to ensure accurate appearance data capture. A directional 0°/45° geometry illuminates the sample at a 0° angle, with the viewing angle set at 45°. Scientific studies show that these geometric principles provide the truest representation of visual color perception.

Today’s spectrophotometers/colorimeters are available in portable, benchtop, and in-line models, designed to monitor color variations and changes in real time, from start to finish. Even slight alterations in color can be detected easily and allow for simple changes to be made at any stage of production, saving wasted materials, time, and money. These simple tools are beneficial for efficiently and effectively creating quality products and increasing sales.

Spectrophotometric Applications in Plastic Manufacturing

The variety in plastic shapes, sizes, and colors can present color measurement challenges. Nonuniformity, gloss, shape, and size can all affect color quantification, so choosing the right solution is the first step in developing consistency and quality in polymer products.

Not only are spectrophotometers/colorimeters effective for enhancing the quality and production of molded plastics, but their versatility also extends to many other areas of plastic manufacturing. For example, even nonuniform plastic pellet samples and recycled polyethylene terephthalate (rPET) can be accurately measured with this equipment. Doing so helps to ensure uniform and consistent pellet color, which is used in extrusion and injection molding and directly affects final color quality.

Other spectrophotometric applications in plastics processing include quantifying color data in:

• Opaque plastic enclosures
• Opaque plastic plaques
• Opaque plastic films
• Opaque sheet plastic
• Dark Performance plastics, such as deep blues, dark charcoal grays, indigos, and blacks
• Vinyl siding

From the beginning stages of plastic production to the final stages of color analysis in sample plaques, spectrophotometry ensures consistency throughout every step of manufacturing. The simplicity and accuracy of today’s advanced instrumentation take the guesswork out of the process, increasing both production and quality overall.

Many quality control (QC) professionals in manufacturing focus on variables like formulations, processing impacts, and contamination when considering which factors cause color alterations in their products. But for certain applications and in extreme environments, one unseen variable can cause equal damage to color consistency — temperature.

Even minor temperature variations can quickly ruin a batch or turn QC into expensive guesswork. The fluctuations can influence a sample's optical properties, alter light interactions, and impact measurement data reliability. As a result, maintaining color confidence in extreme conditions requires both strict protocols and powerful equipment to mitigate the environmental variables and uphold data integrity.

What Causes Temperature to Alter Color Measurement Results?

Understanding how temperature alters measurement results requires examining both the material-level changes and environmental factors that impact spectrophotometric analysis.

Thermochromism

Thermochromism is the phenomenon of a material exhibiting a reversible change of color in response to temperature changes. For example, think of novelty cups that turn from blue to green when filled with hot or cold liquid. This color change isn't the result of user error, but instead a temporary alteration in the material's optical properties that causes the material to reflect or transmit different proportions of light across the visible spectrum.

As the temperature of the contents starts to normalize to room temperature, the original color gradually returns. In such products, these color alterations are the goal for the desired effect. In others, thermochromism is a consequence to avoid, making consistency the key to preventing it. 

It's important not to confuse thermochromism with thermal degradation, an irreversible color change arising from extreme temperatures that can impact long-term color stability.

Environmental Instability and Material State Changes

Extreme temperatures can trigger physical changes in many samples that impact color perception, depending on the application. For example, thermal expansion and contraction can alter surface textures, changing how light reflects off the material and, in turn, the resulting measurements.

Measuring the color of hot liquids poses similar issues. As temperatures rise in these samples, bubbles and vapor often form that cause light to scatter differently, influencing appearance.

Additionally, temperature fluctuations can create secondary effects, such as the formation of condensation on sample surfaces. This excess humidity demands well-defined surface preparation protocols to ensure accurate readings.

The Vista spectrophotometer includes a smart touchscreen display that requires very little operator training. Image Source: HunterLab

We rely on our smartphones for just about everything, from navigation to communication. Messaging apps and texting allow us to instantly talk to everyone from our closest friends to distant relatives, all without ever leaving the house. News and entertainment are just a few taps away, and we have the ability to research any subject imaginable within seconds. All of this is made possible in part by intuitive interfaces and operating systems that make it easy to use this advanced technology on a daily basis. In this sense, smart technology blends seamlessly into our lifestyles, both becoming part of our everyday routine and making that routine easier than ever.

Just as smartphones have changed the way we communicate and interact with the world around us, smart spectrophotometers are changing the possibilities of spectrophotometric color measurement and revolutionizing operators’ work styles. Smart screen displays, advanced data management software, and network communications have made smart spectrophotometers easier to use, enhancing usability of data and efficiency of color analysis.

However, while there have been significant advances in smart spectrophotometer technology, many operators still use outdated instruments. Using a spectrophotometer without state-of-the-art features is a bit like being forced to make calls from a rotary phone—outdated technology slows down workflows and leads to manufacturing inefficiencies and errors. This is why you should consider making the switch to smart spectrophotometers in your lab. Smart technology improves productivity, data management, and operator learning curves, allowing you to maximize your operators’ time and, ultimately, produce higher-quality products.

Smart spectrophotometers like the Aeros improve workflow by speeding up the sample preparation process and making it easier to record measurements. Image Source: HunterLab