Interested in a little light reading?

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.

We use the word “color consistency” a lot when referring to products that depend on this trait for quality assurance. In the pharmaceutical industry, color consistency means a lot more than the final color outcome of a product. Color consistency in pharmaceutical powders and tablets is essential for developing the right drug formulations and repeating these formulas accurately every time.

Although outward appearance and color-coding do have their place in prescription drugs, what consumers and patients are most concerned about is that the active pharmaceutical ingredients will be the precise dosage and formulation they need each time they take a medication. Spectrophotometers measure color consistency to ensure that each powder or tablet formulation attains precisely the correct components for effectiveness and safety.

Image Source: Flickr user Steve Snodgrass

Color isn't just visual—it's emotional. It shapes how we feel about the food we eat and the trust we place in the brands behind it. Now, more than ever, that trust is being tested. With growing evidence that synthetic food dyes like Red No. 40 and Yellow No. 5 may harm children's health, and with global regulators stepping in, food manufacturers face a moral and market imperative: it's time to go natural.

The 2025 Make America Healthy Again (MAHA) Report has sent a clear signal—reformulate or be left behind. But moving away from synthetic dyes isn't just about compliance. It's about delivering safer, cleaner, and emotionally resonant food experiences. And that’s where HunterLab comes in.

Why Synthetic Food Dyes Are Being Banned

From hyperactivity in children to outdated FDA safety standards, synthetic dyes have become a public health concern. The MAHA Report, backed by federal agencies, is pushing for urgent reevaluation. Europe has long since labeled or banned these additives—and the U.S. is finally catching up.

For food brands, the message is clear: if you're still using petrochemical dyes, your products—and your reputation—are at risk.

Scientific Challenges of Going Natural

Switching from synthetic to natural colorants isn’t easy. Food scientists must solve for:

• Stability: Natural dyes degrade in heat, light, or acidic conditions.
• pH Sensitivity: Color shifts based on a product’s pH.
• Flavor Impact: Many natural pigments affect taste.
• Consistency: Batch-to-batch variation in natural ingredients.
• Supply & Cost: Natural colors are costlier and harder to scale.
  

High-quality cookie products should be consistent in color from batch to batch. Image Source: Shutterstock user Natali Zakharova

Few people can resist nibbling on a perfectly-baked cookie. Many find the mouthwatering, nostalgic aromas of caramelized sugar coupled with the rich golden brown crumbles downright irresistible. But if you’ve ever eaten an under or overbaked cookie, you know that not all cookies are as delicious as they should be. Factors like setting the oven temperature too high or too low or baking the cookies for too long or too little time could negatively impact the texture and color of the cookie as well as someone’s experience eating it.

This is why large-scale cookie manufacturers need to carefully measure the color of their cookie products. Using a smart spectrophotometer that is capable of accurately measuring the color of textured samples (like crumbly cookies), you can ensure that every batch of cookies is baked to perfection and that they all appear uniform in color to your customers. Whether you produce just a few thousand packages of gourmet cookies every year, or you make millions of cookies in a wide variety of flavors and textures, a smart spectrophotometer can help you refine your manufacturing process.

Color is a Sign of Cookie Quality

The color of cookies and other baked foods can tell you a great deal about how the product will likely taste. This is due to caramelization and the Maillard reaction, a complex chemical process that causes food to turn brown as it’s exposed to heat.1 During the Maillard reaction, the proteins and sugars in the food are broken down by high temperatures, which results in deeper coloration and a significant change in flavor and aroma. In the case of cookies, the Maillard reaction browns the color of the raw cookie dough and produces strong aromatic compounds—that classic freshly-baked cookie scent.

For cookie manufacturers, paying close attention to caramelization and the Maillard reaction is important because too much exposure to heat over time could result in an overly bitter, brittle cookie. Likewise, too little heat exposure will impede the development of the Maillard reaction or caramelization, and the cookie will be soft, pale, and somewhat bland in flavor. Customers are aware of the connection between cookie color, texture, and quality, and the appearance of the cookie may impact a customer’s buying habits.2 This is why you need a smart spectrophotometer to ensure that all of your cookie products have gone through just the right amount of caramelization and appear consistent in color overall.

Significant variations in cookie color could be a sign that your industrial oven temperature is set too high or too low. Image Source: Shutterstock user Brent Hofacker

Spectrophotometers measure wavelengths of light emitted from samples to ensure product consistency, desired color output, and other industry-relevant factors. 

What Is Reflectance?

Reflectance can be defined as the ratio of reflected to incident radiation, and it's an essential measurement in several fields. It corresponds to the amount of light that your sample reflects (emits) as compared to a specific reference material. Reflectance color measurement is required samples that are opaque as apposed to translucent or transparent. 

The percentage you get when measuring reflectance is a spectrum of reflection percentage per wavelength or nanometer (nm). For example, if you test a red sample with white light, the expected spectrum should hit the maximum reflectance, usually around 700 nanometers for red visible spectra. 

How to Measure Reflectance

A spectrophotometer attains a measurement of reflectivity by fulfilling the following actions: 

1. The spectrophotometer transmits all the wavelengths of light while shining a light on the sample. 
2. It measures the light that the sample reflects back. 
3. It converts that measurement into a quantified graph showing the dominant wavelengths of the color reflectance. 

The reflectance consists of diffuse reflected light and specular reflected light. 

Diffuse reflected light is the permeating light that scatters in a variety of directions, observed when light beams reflect from microscopically rough surfaces.

Specular reflected light reflects at the same angle as the incident angle of light, creating a mirror image. Essentially, this beam of light when reflecting off of smooth surfaces remains as a beam of light. 

The Purpose of Measuring Reflectance

Reflectance measurement shows which part of the light spectrum a particular object belongs to. Humans have evolved to see a small part of the spectrum, known as visible light. The range of visible light stops at around 700 nanometers, but most of the light spectrum falls outside that continuum. 

Measuring reflectance ensures that an item meets the aesthetic and quality control requirements of various items. It shows the dominant wavelengths that allow you to check that the product meets the desired wavelength range. Here are the typical wavelength ranges of different colors: 

• Yellow: 570-585 nm
• Blue: 440-490 nm
• Indigo: 420-440 nm
• Red: 620-780 nm
• Orange: 585-620 nm
• Green: 490-570 nm
• Violet: 400-420 nm

Every material absorbs, reflects, or transmits light, which determines the color we see when looking at an object. Transmission refers to the light waves that pass through a translucent or transparent sample, and spectrophotometers provide quantitative measurements of that data. These devices make it possible to evaluate a sample's color scientifically and objectively, which is vital for ensuring color consistency in various applications. Spectrophotometer transmittance measurements enable better quality control and enhanced consumer perception of your products.

What Is Transmittance in a Spectrophotometer?

The definition of transmittance is the measured light that passes through a sample, meaning the light that is not absorbed or reflected. Three primary transmittance measurements include:

• Diffuse transmittance (Td, n): This measurement is the ratio of the flux transmitted by a specimen to the incident flux, with the transmitted flux being measured at all forward angles except the regular transmission angle. When light is diffusely transmitted, its direction changes as it passes through the material, causing scattering.
• Regular transmittance (tr, n): This measurement is the ratio of undiffused transmitted flux to incident flux. In other words, it is straight-through light.
• Total transmittance (tt, n): This measurement is the ratio of the flux transmitted at all forward angles to the incident flux. Total transmittance is the sum of regular transmittance and diffuse transmission.

These values are essential to maintaining quality in products like beverages and edible oils. It's best to measure color with a spectrophotometer to capture more accurate information, as these devices provide exact quantitative data regarding the amount of light that passes through a sample. 

The transmittance formula is:

T = PT/P0

The values in this formula represent:

• T: Transmittance
• PT: The source's radiation power as it exits the sample
• P0: The source's radiation power as it enters the sample

The resulting calculation is a ratio, comparing the light before it enters the sample to the light after it passes through it. A value closer to 1 means most light passes through, while lower values mean that less light passes through. 

What Is Percent Transmittance in a Spectrophotometer?

Percent transmittance displays the light that passes through the sample as a percentage rather than the ratio created by the above formula. You can get the value by multiplying the ratio by 100. 

A sample with 100% transmittance is transparent, allowing all light to pass through. Lower numbers indicate more translucence than transparency. At least 30% of the light must pass through the material for effective transmittance measurements.

The transmission percentage is also helpful for absorbance calculations. A commonly used absorbance formula is:

A = 2-log10(%T)

This formula determines the amount of light absorbed using the percentage of light that passes through the sample. 

Resin samples typically measured in Gardner Color

The APHA/Pt-Co/Hazen and Gardner visual color scales were both originally based on liquid chloroplatinate color standards but have different history and intended use.