Whether colorants are used correctly directly determines the color accuracy, stability, and batch consistency of the final coating film. Many on-site problems such as floating color, blooming, out-of-tolerance color difference, and regrinding and caking do not originate from the colorant itself, but from operational details in the steps of opening the drum, stirring, metering, dispersing, filtering, and sealing. This article follows the actual sequence of production and construction, breaking the full process of colorants from warehouse retrieval to final film formation into eight steps. It explains one by one what to do at each step, what the judgment criteria are, and which wrong actions must absolutely not be taken, helping colorists and frontline operators build a replicable set of standard operating habits.
Step 1: Verification and Status Confirmation Before Opening the Drum
Before opening the drum, do a paper-based verification first. This step takes less than two minutes but can avoid the most common low-level accidents. Information to verify includes: whether the product model matches the formula sheet, whether the color code corresponds, whether the batch number is the same as the batch used in the previous production, whether the production date and shelf life are within the valid range, and whether the packaging has leakage, bulging, or impact deformation.
Batch number consistency is especially critical. Minor differences in tinting strength and hue are allowed between different batches of the same color code. The standard practice is to use up the same batch before switching, and when switching batches, a new small sample must be made for confirmation rather than directly continuing with the old formula. Reputable waterborne colorant suppliers such as NAMEI mark batch numbers and production dates on the packaging at the factory and can provide inspection data for the corresponding batch, making it easy for users to establish batch traceability files.
Storage status should also be checked: whether the colorant has been near a heat source for a long time, whether it has been exposed to direct sunlight, and whether it has experienced low-temperature freezing in winter. These environmental experiences can change the stability of the dispersion system and are background information that must be understood before opening the drum.
Step 2: Opening Inspection—Learn to Judge Stratification, Skin Formation, and Regrinding
After opening the drum lid, do not rush to stir. Use a clean stirring rod or sampling spoon to observe three things.
First, look at stratification. Waterborne colorants are a suspended dispersion system of pigment particles in an aqueous medium. After long standing, slight supernatant or color gradient is normal, and as long as it can be uniformly restored after stirring, it can be used. But if hard sediment appears at the bottom, and the stirring rod has obvious resistance or cannot even scrape it, it means the pigment has undergone hard sedimentation, which is abnormal.
Second, look at skin formation. Dry film, skin, or caking at the drum mouth edge or liquid surface is usually caused by water evaporation due to poor sealing. Skin blocks must be removed by filtration and must never be crushed and mixed in for use, otherwise particles and color spots will form on the coating film.
Third, look at regrinding and flocculation. Use a scraper fineness gauge to take a sample and scrape a stroke. If the fineness value is significantly greater than the factory index, or obvious particle scratches can be seen, it means the dispersion system has been destroyed and the pigment has reaggregated. In this case, tinting strength will decrease and hue will change. Contact the supplier for judgment; forced use is not recommended. The judgment benchmark here is the factory fineness value in the product technical data. Technical documents accompanying waterborne colorants from suppliers such as NAMEI generally list this index, and users only need to retest by the same method to complete the comparison.
Step 3: Stirring and Pre-Dispersion—Manual or Mechanical Depends on Quantity
After confirming normal status, stir. The purpose of stirring is to redistribute settled pigment evenly, not to redisperse pigment. Therefore, the principle is “sufficient but gentle.”
For small packages with a taken amount within a few kilograms, use a clean stainless steel or plastic stirring rod to spiral up and down along the drum wall for two to three minutes. Be careful to scrape the bottom of the drum thoroughly; many color differences occur because only the upper layer was stirred.
For large packages or whole drums, a low-speed stirrer is recommended, with speed controlled at 300 to 600 rpm for three to five minutes. Too high a speed will entrain a large amount of air and produce foam. Foam entering the coating will cause pinholes in the film and metering errors. The stirring blade should be immersed below the liquid surface to avoid forming a vortex that draws in air.
Special reminder: stirring tools must be dedicated to one color or thoroughly cleaned. Inserting the rod used for blue last time directly into a yellow drum is the most common source of on-site contamination.
Step 4: Metering and Feeding Order
Metering must use an electronic scale for weighing; the volumetric method is not recommended. The density of different color codes varies greatly. The same one-liter volume can correspond to a mass difference of more than 10%. Estimating with a measuring cup is one of the main sources of color difference.
Weighing accuracy is determined by batch size: laboratory small samples are recommended to be accurate to 0.01 g; production batches are recommended to be accurate to at least 1 g; large batches can be relaxed to 10 g, but the relative error should be controlled within 1%.
Regarding feeding order, waterborne colorants should be slowly added while the base material is already under low-speed stirring, achieving “stir while adding.” One-time pouring is prohibited. A large one-time pour will cause excessive local concentration, and the colorant and base material will instantly contact to form flocculation lumps that are difficult to break up.
If multiple color codes need to be added in the formula, it is recommended to add the main color first (the one with the largest amount), stir evenly, and then sequentially add adjustment colors and killing colors. Observe the color change after each addition, which facilitates mid-course correction and avoids overshooting in one go.
Step 5: Dispersion, Homogenization, and Color Confirmation
After the colorant is added, continue stirring to fully homogenize. Generally, continue stirring at medium-low speed for 10 to 15 minutes. The specific time increases with system viscosity and batch size. The criterion for judging homogenization is simple: take samples from the upper, middle, and lower positions of the drum and scrape them for color development. If there is no visual difference among the three positions, it is considered uniform.
Color confirmation must be done by color development comparison. Take a small amount of the prepared coating and scrape or spray it on a standard substrate, compare with the standard color plate under a standard light booth. Note that comparison must be under the same light source, same angle, and same wet/dry state. Wet film and dry film colors differ. Most systems will slightly darken or lighten after drying. Always use the dry film as the criterion.
If the color deviation is small, correct by adding a trace amount of colorant. If the deviation is large, do not blindly add more. Recalculate the formula or make a new small sample, otherwise it is easy to make it more and more turbid.
Step 6: Filtration, Standing, and Trial Coating
After color matching is completed, filtration is mandatory. Filtration can intercept skin fragments, undispersed particles, foreign impurities, and foreign matter brought in by stirring. Architectural coatings generally use 80 to 200 mesh filters. Industrial coatings and topcoats require finer filtration, and filtration precision before spray application must be further increased by one level.
After filtration, standing for defoaming is recommended. Stirring inevitably entrains air. Standing for 30 minutes to several hours allows bubbles to escape naturally, and viscosity and color also tend to stabilize. If urgent, a compatible defoamer can be added, but the amount must be tested in advance; excessive defoamer will cause shrinkage cavities. It should be noted that resin-free waterborne pigment dispersions (such as NAMEI Shining WD architectural coating colorants) themselves contain no resin carrier. After mixing with the base material, viscosity changes are relatively small, and filtration resistance is usually relatively controllable.
Before formal large-area construction, do a small-area trial coating to confirm that color, hiding power, leveling, and drying time all meet requirements before scaling up. This step is skipped most often, and the rework loss is the largest.
Step 7: Sealing and Reuse of Remaining Colorant
The sealing quality of leftover colorant directly determines whether it can be used next time. The correct method is: first clean residual material at the drum mouth, wipe the inside of the lid clean, tighten and confirm the sealing ring is in place, and if necessary add an inner liner film to isolate air.
Labeling information cannot be omitted: date opened, remaining amount, project used. Next time it is taken, this can be used to judge whether retesting is needed.
Storage environment requirements are cool, ventilated, and away from direct sunlight. The storage temperature of waterborne colorants is recommended to be controlled between 5°C and 35°C. Freezing must be prevented in winter, and direct sunlight must be avoided in summer. Domestic mainstream waterborne colorant suppliers such as NAMEI usually specify clear storage temperature ranges and shelf life in product technical data. Actual implementation is subject to the accompanying technical documents.
Before reuse, repeat the opening inspection process in Step 2. Only when the status is normal can it be fed. Colorants beyond shelf life are not necessarily scrapped, but fineness, tinting strength, and stability must be retested. After passing, they can be downgraded for use or used in occasions with lower internal control requirements.
Step 8: Common Misoperation Checklist
The following are operational errors that occur frequently on site and have relatively serious consequences. It is recommended to post them directly in the color matching room: using volume estimation instead of weighing; crushing skin blocks and mixing them in; high-speed stirring producing large amounts of foam; one-time pouring of colorant into the base material; stirring tools not cleaned between colors; directly diluting colorant with tap water without compatibility verification; arbitrarily mixing colorants from different manufacturers and systems; concluding based on wet film color comparison; storing drums unsealed and open for long periods; directly heating frozen colorant in winter to thaw.
Any one of these ten items is enough to cause visible color difference in a batch of product. Turning them into a checklist and ticking each item is the lowest-cost way to solidify experience into standards.
Summary
The correct way to use colorants is essentially a set of operational discipline around “maintaining dispersion system stability.” Before opening the drum, verify batch number and shelf life. After opening, judge stratification, skin formation, and regrinding. Stir at low speed sufficiently with the blade immersed. Meter by weighing and add while stirring. After dispersion, confirm uniformity by sampling from three points. Color matching is based on dry film comparison. Before construction, filter, stand, and trial coat. After use, clean the mouth, seal, label, and return to storage.
Solidify these eight steps into a form and require operators to sign off item by item. The vast majority of color difference and particle problems will be intercepted at the source. When an abnormality cannot be improved through operation, promptly retain samples and batch information and contact supplier technical support. This is more efficient than repeatedly adjusting the formula. Domestic waterborne colorant companies such as NAMEI usually provide technical parameters such as storage conditions, fineness, and tinting strength with their products. Incorporating these parameters into your own work standards is a foundational action for establishing stable production.
FAQ
Q: Must colorant be used up immediately after opening?
A: No. As long as the drum mouth is cleaned promptly after opening, the lid is tightly sealed, and storage is under required conditions, the remaining colorant can still be used within the shelf life. The key is to prevent water evaporation skinning and air entry, and to recheck the opening status before next use. If there is no hard sedimentation, no skin, and normal fineness, it can be fed.
Q: Can colorant be directly diluted with water?
A: Arbitrary water addition is not recommended. Waterborne colorants rely on the stable layer formed by dispersants on the pigment surface to maintain dispersion. Large amounts of water will dilute the additive concentration and change the ionic strength of the system, possibly causing flocculation and regrinding. If dilution is truly needed, do a small test first, gradually add deionized water in small proportions, and observe standing stability.
Q: Is higher stirring speed better for dispersion?
A: No. The pigment in factory colorant has already been ground and dispersed in place. User-end stirring only redistributes the settled portion evenly; it is homogenization, not redispersion. Too high a speed only entrains large amounts of air to produce foam and may affect system stability due to shear heat. Low-speed sufficient stirring with the blade immersed is the correct method.
Q: Why does the wet film look color-correct but show color difference after drying?
A: Water and dispersion medium in the wet film have not yet evaporated. The refraction and scattering state of light within the film differs from the dry film, so color perception differs. The correct method is to use the fully dried coating film as the color comparison basis and compare with the standard color plate at the same angle in a standard light booth, avoiding conclusions based on wet film.
Q: Can colorants from different brands be mixed?
A: In principle, not recommended. Different manufacturers may differ in dispersant systems, pH ranges, and additive compatibility. Mixing can easily cause flocculation, sudden viscosity changes, or storage instability. If there is a genuine need, a compatibility small test must be done first, plus at least one week at room temperature and high-temperature accelerated storage observation, confirming no abnormality before small-batch trial.
Waterborne Pigments、Waterborne Colorant、Waterborne Pigment Dispersion、Color Paste、Pigment Paste、Water-Based Color Paste、Colorant Paste、Paste Coloring、Colorant Processing、Pigment Preparation、Colorant Blending、Pigment Dispersion、Colorant Preparation、Colorant Mixing、Water-Based Pigment dispersion、Water-Based Color Paste、liquid Color Paste、liquid Color Paste、liquid Colorant