Why did it change?
Let's first look at an principe:
White ink base--Form a "canvas"--Print spot color ink on the "canvas"
As can be seen from the above principe, the spot color effect relies on a complex physical process involving light, ink and white background:
The change of the underlying "canvas" (the main reason):
Uncoated white (printed directly on the transparent film): The spot color ink comes into direct contact with the transparent film. Light passes through the ink and the film, with some being absorbed and some passing through, resulting in an unsaturated color, a grayish tint, and a dim appearance. It is also affected by the color of the underlying item.
With the white overlay: The white base layer is like a brand-new blank sheet of paper, providing a uniform, opaque, and highly reflective foundation. After the light is fully reflected on the white layer, it passes through the spot color ink again, significantly enhancing the saturation, brightness, coverage, and accuracy of the colors.
The physical properties of ink:
The spot color ink has a certain degree of transparency by itself. After padding with white, the white background will undergo optical mixing with the upper layer of the spot color ink, similar to the influence of "background color" on "upper color" in painting.
Even with the same formula ink, when printed on different backgrounds (transparent vs pure white), the final spectral reflection perceived by the human eye will be different.
What specific changes will there be?
Changes towards a more vivid and saturated direction (usually a positive change):
Pure colors such as red, yellow and blue will become extremely bright, lustrous and rich in texture.
This is the primary purpose of the "white overlay" - to restore the colors that the designer sees on the computer (with the default background being white).
The hue may experience a slight deviation (which requires careful control):
For instance, certain specific shades of purple, dark blue, and dark green may become slightly cooler or warmer when a white background is added.
The variations of metallic colors (such as special gold and special silver) are particularly noticeable. Without a backing layer, the metallic luster directly reflects the light, resulting in a strong but thin effect; with a backing layer, the metallic particles are highlighted by the white color, making the color more vibrant, but the metallic luster will be weakened, resembling "solid gold".
Coverage becomes absolutely (fundamentally improved):
Without a padding layer, dark text may show traces of the underlying background in the light-colored areas. With a padding layer added, the white layer completely blocks out the background, making the text and image boundaries clear and sharp, and the colors pure.
Our professional solution (for promoting the factory's capabilities)
As a professional plastic packaging bag factory, we will definitely not allow such changes to become an "accident". Our process ensures that color variations are completely under control:
Standardized proofing process:
When the design draft specifies spot colors, we will definitely ask: "Do we need a white overlay?" . We will recommend the best solution based on your final usage scenario (what products will be packaged? Do you need a transparent window?)
During the proofing process, we offer a comparison sample of "with white padding" and "without white padding", allowing you to see the difference for yourself and confirm whether the effect after adding white padding meets your expectations.
Strict ink management:
We adopt the standardized spot color ink systems of international brands (such as DIC and Pantone), and establish our own laboratory color matching database.
For the special colors that require a white overlay, our experienced color-mixing technicians will make minor adjustments to the formula of the upper layer of special color inks based on the characteristics of the white base ink, in order to closely approximate the effect of your specified Pantone color code on standard white paper.
Advanced printing and quality inspection:
Our printing machine is equipped with an online color scanning system, which can monitor the spot color density and Lab values in real time.
For the spot colors after the white overlay, we will re-color them based on the white overlay sample bag that you have confirmed, rather than simply comparing with the Pantone color chart.
In conclusion, adding white padding is a standard and necessary process in plastic packaging printing to enhance the quality of spot colors. As long as you collaborate with a factory like ours that has professional color management capabilities, this "change" will transform from a risk into a certain advantage that will make your packaging stand out.