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Coloring Plastic Lenses, Section 2


lenses should be mounted in the lens holder so that they are not under pressure. Any pressure exerted upon a lens at tint solution temperatures may cause warping. Lens holders that are spring loaded or place tension on the lenses in any other way should not be used.
Be sure that the lens coloring system is operating at the correct temperature. Put the lenses s-l-o-w-l-y into the color tank. We recommend lenses be placed into the tank slowly because piercing the surface tension too quickly may cause a boil-over.
Tinting times are a function of lens cure, tint concentration and temperature. A general timing chart is provided as a starting point; however your own experience will determine the optimum immersion period more exactly.
After the lenses have been tinted to the desired color, it is suggested that they be put in the Lens Prep II™ solution again, to allow excess tint to come off more easily.
Rinse under cool tap water or in a beaker of water. The lenses should be wiped with a very soft lint-free cloth or Kaydry™ to avoid scratches.
Removing Molecular Catalytic™ tint is achieved quickly by using BPI® Neutralizer II™. This is a strong agent which will remove the color from the lens in about twice the time the lens took to tint. There may be variations in time, because the lenses are not all made to the same formula and specifications, but the lenses will come back to an almost clear color. Try BPI® PolyClear™ for coated lenses.
If one lens is darker than its mate, then either the darker lens could be neutralized, or the lighter lens could be put into the tint tank unit until it has attained the proper color.


BLOTCHING, CIRCLE LIKE EFFECTS: Blotching, circles, or half-moon effects are the result of tinting a lens that has been unevenly cured. This means that the density of the lattice structure (lens hardness) varies. The soft parts of the lens will accept tint more quickly and become darker, resulting in unevenness of color.
A blotch indicates premature release of the lens from the casting mold. Circles are caused by the rubber gasket material having had an insulating effect on the lens while it was being cured, resulting in a looser lattice structure of the outer edge. These areas will tint darker, as they are softer.
A partial solution, should you not desire to go back to the lens manufacturer, may be brought about by immersion of the lenses into HOT Neutralizer II™. Or, if you have a BPI® Lab Fuser™ (Diffusion Oven), you may essentially "recure" the lens by placing it into the oven for about 15-20 minutes at 240°F., thus tightening its lattice structure to allow a more even coloring of the lens.

COLOR VARIATIONS: If you are using TAP WATER, the mineral content may cause color deviations. Also, the chlorine tends to "kill" the red side of the spectrum, resulting in aqua or blue-toned "grays" and olive-toned "browns". It is recommended that de-ionized or distilled water be used, where possible, in lieu of tap water to eliminate this problem. Drawing your water the night before and exposing it to the atmosphere will dissipate the chlorine.
If you have inadvertently dripped heat transfer fluid, heat transfer fluid, from the outside of your tint tanks when moving them, the color in which it dripped will be lacking some of the red, causing some of the above described color variations. Also, when washing out your tint tanks prior to mixing a new batch of tint, make sure none of the heat transfer fluid from the outside of the tank is transferred to the inside of it. It is good to rinse tanks under running water for 5-10 minutes after washing them.

PURPLE OVERTONES AND RED FLARES: When your lenses have a PURPLE overtone, it is generally the result of the tint having been mixed with water for too long. The oxygen content of the water interacts with the tint chemistry causing this purplish appearance. To correct, add yellow tint directly from the bottle (or proportionately more if already diluted). Check your corrections as you go along so you will not add too much yellow.
When you have a RED or PINKISH overtone, particularly in dark grays or dark browns, there are several things to be considered. Do you have a very hard lens? A longer tinting time will be needed, and to avoid picking up too much of the red pigment from gray or brown, make sure the tint solution has enough of the blue to counteract the red.
Are you using the whole bottle? Mixed colors may settle in layers, especially after long storage. Be sure to shake well and rinse out each tint bottle until the water runs clear, to obtain the correct shade.
Are you surpassing the color standard? If you are trying for too dark a shade with a tint formulated for lighter shades, the lens will exhibit the red appearance. Make sure the tint is appropriate to the density desired in the finished result.
You may obtain better results using colors specifically made for deeper densities with minimal or no red flare at color standard. For sunglass shades in the BROWN family, choose Autumn Brown™ with its gray overtone, Swiss Chocolate™ or Sun Brown™; for GRAYS, BPI® Black™ or Sun Gray™ is preferred.
For a darker gray, another solution would be first to immerse the lens to obtain a light blue, then dip into gray. For a darker brown, get a light green, then dip into brown. Alternatively, use BPI® Red Out™ for a one step correction. Dip a gray or brown lens with a red tone into Red Out™ until the desired color is achieved.

PITTED LENSES: Occasionally, customers have sent lenses to us which show a pitted or bubbled appearance after a tinting or neutralizing procedure. The lenses we have examined show such pits are a weakness of the lens in a small spot, probably caused by either: Co-polymerization with oil on the surface of the mold, or a spatter of solvent.
While such weaknesses are usually nearly invisible, they become apparent because they absorb water and Neutralizer II™ during: Repeated neutralizing and tinting, or alternation of Neutralizer II™, water and/or Lens Prep II™, or subjection to repeated thermal shock. (Extremes of hot and cold)
The solutions are as follows: In general with these lenses, avoid repeated neutralizing at high temperatures; let the lenses cool down slowly and without water, allowing the Neutralizer to remain on them, and, when cooled, wash in water and wipe dry with non-abrasive, lint-free cloth or tissues (such as Mini-Kaydrys™).
In extreme cases when no other recourse is available, a lens may be salvaged by neutralizing it completely, letting it cool down with Neutralizer II™ on it, wiping it when cool and then heating it slowly in an oven (such as the BPI® Lab Fuser™) to about 250°F.
STREAKS: In a tint solution which has not been used for some while, or used less often than others, the pigment may separate from the water, causing a clumping together of tint pigment or agglomerations. Use of BPI® Color Developer™ as directed will help eliminate streaking due to this. Also, periodically heating and stirring your tints when they are not in active use will help keep them properly suspended. Other causes of streaks:

  • heat transfer fluid tint contamination.

  • Lens holders with accumulated tint residue.

  • Lens Prep II™ in too high a concentration, resulting in unevenness of color or streaking in the same area after a second coloring of the lens.

  • Varying lens hardness.


Lattice structure refers to the density of the lens. A lens with a loose lattice structure is referred to as a "soft" lens and will tint rapidly. Conversely, one with a tight lattice structure, or a hard lens, will take longer.
Even though your lenses are from the same manufacturer, there may be a difference in their hardness. Each batch run may have lenses which have been subjected to variations in relative position in the curing oven, temperatures to which they have been exposed, and the length of time cured.
The longer the cure, the harder the lens. There is little probability of getting lenses from the same batch run on a consistent bases.
The mixing of surfaced and stock lenses should also be avoided as much as possible, as the surfaced lenses, which began as a much thicker blank, have been cured differently and will accept tint differently.
Lattice structure, tint solution temperature, prior preparation with Lens Prep II™, and scratch resistant coatings all affect the coloring times.
The harder the lens, or the lower the temperature, the longer it will take to tint it. Darker colors will take longer. The hotter the tint, the faster results will be obtained. We recommend a minimum of 200°F., but for dark shades, tint solutions as hot as 210°F have been used.


Be sure to use Lens Prep II™. More than just a surface cleaner, it conditions the lens surface. Lens Prep II™ is used one capful to a quart of water and should be changed every 3-4 days, depending on use. Do not rinse or wipe lens after using Lens Prep II™; to do so will negate its effectiveness.

BPI® COLOR DEVELOPER™: Injudicious use of BPI® Color Developer™ may cause color changes. The effectiveness of Color Developer™ is so great that only a drop or two every other day need be used. Overuse of this concentrate will cause a loss of the red side of the spectrum. Since Color Developer™ is used primarily as a re-suspending agent for tints infrequently used, this chemical will not likely be used in your grays or browns, which are used more often. To correct a brown, black or gray tint solution which shows a blue/green overtone, add pink or red a little at a time until proper color balance is restored.

GENERAL PRINCIPLES: All colors, particularly dark grays, should be examined by daylight or special bulbs. Most fluorescent or incandescent lights will make the shades of tinted lenses appear more blue or red than they look in daylight. The dilution factor when using larger bottles of concentrate is approximately one part tint to ten parts water (preferable de-ionized or distilled).
Probably the most important thing to remember when using the larger bottles of concentrate is that the pigment will settle to the bottom of the bottle during storage and that THOROUGH MIXING of the tint in its bottle must be done BEFORE pouring out a part to be diluted. The reason for this is that layers of pigment will settle to the bottom of the bottle during storage.
In order to maintain the color standard throughout the use of the bottle, it must be well mixed. By adding a couple of ordinary glass marbles to each bottle, you can facilitate mixing. Storing these bottles on the side so pigment settles over a wider area results in thinner layers which are more easily mixed. Failure to shake these containers well will result in a reddish cast during the first part of the use of the bottle, and a blue-green cast during the use of the last part. It should be remembered that tint is more economically purchased in these larger containers only if that amount will be used within the recommended shelf life of 6 months. For those who normally tint a dozen or so lenses daily, the small 3 oz. container of concentrate has been shown to be more economical. It should be noted that, since the larger sized bottles are specially ordered, they cannot be returned.