Note: Descriptions are shown in the official language in which they were submitted.
~7~S~9
This application is a divisional of copending Canadian applica-
tion Serial Number 3680G8 filed January 7 1981, Messrs Meshel and Gregory,
which is in turn a divisional of application Serial Number 283867, now
Canadian Patent Number 1095755 which issued on February 17, 1981 to
Meshel and Gregory.
A conventional soft or flexible contact lens is formed of a
hydrated gel polymer, commonly polyhydroxyethyl methacrylate (HEMA).
Various attempts have been made to color such lenses as with vegetable
coloring, earth pigments, and water insoluble marking pigments. However,
these methods have not been successful as the pigments may leach out of
the lens and irritate the eye. Furthermore, some pigments are readily
removed by soaking solution or boiling.
In accordance with the present invention, a colored image is
formed in a limited area of a soft hydrated gel contact lens. In one
method, the lens is soaked in a diazonium salt solution and is there-
after exposed to actinic light through a mask which transmits light
only to the non-image area of the lens. Thereafter, the unexposed
image area is developed by soaking the lens in an aqueous solution of
azo coupler. This method is particularly adapted to forming large
images such as of the patient's iris.
In another technique, an aqueous solution of the diazonium
salt in a gel relief of the desired image is contacted with the soft
lens to form a latent image of the relief. Then, the image is
developed by contacting the lens with an aqueous solution!of azo
coupler. The order of application of the diazonium salt and azo coupler
may be reversed in this latter procedure.
.
~.
~ ~7~
In a third technique, an aqueous azo dye solution is preformed
including a diazonium salt, an azo coupler, and a coupling inhibitor
~- (a pH reducing agent). This solution is soaked into a gel relief of the
foregoing type and contacted with a soft lens to form a latent image.
The image is developed by increasing the p~l in its area of the lens to
a level conducive to coupling. Exposure to ammonia gas is preferred as
it avoids extensive contact of the lens with a potentially harm~ul base
solution. Apparatus is provided for precise alignment of the symbols
deposited on the lens from the gel relief. It includes one or mo~e
striker arms, preferably resilient, carrying said relief images and
which are movable toward and away from a lens retained on a contact
surface. ;In one embodiment, the striker arms are carried by a rotating
wheel for rapid deposition of multiple coded symbols on different lenses.
Also, enlarged coding means may be provided for ready visibility of the
symbol to be deposited.
It is an object of the invention to provide a rapid, effective
method for the permanent deposition of a precise colored image on a soft
contact lens.
It is a further object of the lnvention to provide a method
of the foregoing type in which there is no dstrimental affect upon the
lens.
It is a specific object of the invention to apply diazo dye
techniques to the permanent coloring of a soft contact lens.
According to a broad aspect of the present invention, there
is provided in a method for forming a colored image in a limited area
of 2 soft hydrated gel contact lens, the steps of:
t~1~9
(a) soaking the lens in a solution of a diazonium salt for
sufficient time for said salt to permeate and disperse throughout the
lens gel matrix.
~ b) exposing the soaked lens to actinic light through a photomask
. whîch transmits light to only the non-image area of the lens, the
intensity and time of exposure in the non-image area being sufficient to
decompose the diazonium salt therein to prevent the coupling reaction in
step (c),
~ c) developing the unexposed image area of said lens by soaking
the lens in an aqueous solution of an azo coupler for sufficient time
for the azo coupler to permeate the gel matrix and couple with the un-
decomposed diazonium salt dispersed therein.
The present inventionJthat of copending application Serial
Number 36~068 and that of Patent Number 1095755 will now be described
in greater detail with reference to the accompanying drawings in
which:
Figure 1 is a striker arm strip containing a relief image for
coloring a soft contact lens in accordance with the present invention;
Figure 2 is a side elevational view o~ an apparatus including
multiple striker arm strips on a wheel for sequential application o~
coded symbols to a contact lens; and
Figure 3 is an end view of the apparatus of Figure 2.
The present invention relates to the formation of a colored image
r7~
in a limited area of a soft (i.e., flexible) hydrated gel contact lcns. The
most widely used ~ype of such flexible lens are sold under the trademark
"SO~LENS" by Bausch ~ Lomb. Such lenses are formed of hydrated polyhydroxyethyl
methacrylate. The properties of such lenses are weil known. In its -fully hyd-
rated condition (about 39% water by weight) the lens is soft and supple.
Typically, the lenses are packaged in a sterile condition in normal saline sol-
ution.
Soft lenses are sized to overlap the white area of the eye. Accord-
ingly, for cosmetic reasons~ coloring of the contact lens, as for cutting glare,
must be done selectively so that the colored portion of the lens covers only
the iris of ~he eye during wear.
The following technique for coloring the lens, designated "the
photomask method" is particularl~ adapted for coloring such an image area of
relatively large size and in which an a~solutely sharp boundary is not essential.
In the first step, the lens is soaked or immersed in a solution of a diazonium
salt for sufficient ~ime for the salt to permeate and disperse throughout the
gel matrix of the contact lens. The precise length of time for immersion de-
peD~3 on the ~.emperature and type of dye. At room temperature, a time of one-
half hour to one hour has been found to be a sufficient period.
It is known that diazonium salts are stabilized in a mildly acid
solution, say at a pH of 6 to 7. Suitably, a low concentration of an acid such
as hydroc}lloric acid may be included for this purpose.
After soaking in diazonium salt, the lens is precisely positioned
at a fixed distance from a source of actinic light. Then, a pho~omask is
placed bet~een the ligh-t source and lens ~hich transmits ligllt only to the
arca surrounding the desircd image area of thc lens. Thus, to dye only a cen-
tral area of the lcns, light is transmitted only to the periphery of the cen-
tral area. A suitable mask includes a black form on a transparen~ base.
-- 4 --
~7~
The effect of exposure is to clecompose the diazonium salt to a suf-
ficient extent that the exposec!area will not form a color when the lens is sub-
sequently developed with an azo coupler, Thus, the intensity and time of
exposure should be sufficient for this purpose. A preferred source of actinic
light emits radiation in the ultraviolet range. An effective intensity of ex-
posure is from a 100 watt mercury vt*or lamp at a distance of one foot in an
exposure time-of 5-10 minutes.
After the exposure step, the unexposed area in the form of the de-
sired image is developed by soaking the lens in an aclueous solution of an azo
coupler which foTms the desired color when combined with the selected diazonium
salt.
It is known that the coupling of diazonium salt such as used in
diazo-type photocopying processes is preferably perormed at a slightly alka-
line pH levelJ e.g., a pH of 7 to 8. ThusJ the azo coupler preferably is dis-
solved in an aqueous solution maintained at that pH level. Ef~ective pH ad-
justing agents for this purpose include alkaline salts such as sodium borate,
sodium acetateJ sodium carbonateJ or sodium bicarbonate. AltcrnativelyJ a
non-salt such as a 1% ammonia solution may also be employed.
Sllfficient tlme should be permitted for the development step so
that the azo cuupler pe~meates the gel matrix and couples with essentially all
decomposed diazonium salt dispersccl therein. Although such timing is dependent
upon the part;cular azo couplerJ it has been found that immersion of the lens in
the coupler solution will develop the desired dye in about 5 minutes or more.
After the development stepJ the lens is washed in distilled water
to remove reactants in the coloring procedure. Then~ the lens is boiled in
normal saline solution to render it more compatible with the fluids of the eye.
It has been found that by following the above procedureJ a soft
-- 5 --
7~L9~
contact lens is colored with a substantially fixed non-leacha~le dye. The
color of this fixed or permancnt dye is determined by the combination of dia-
zonium salt and azo coupler which is employed. For e~ample, it has been found
that a single dye may be formed into a variety of colors depending upon the
selection of azo couplers.
Any of a large variety of diazonium salts such as used in diazo-
type photocopying processes may be employed to color the soft contact lenses.
The art is highly developed with respect to aromatic diazo compounds. Ilnder acid
condition, these compounds exist as diazonium salts. ~'articularly effective
diazonium salts for purpose of the present invention include one or more of the
followings compounds:
DIAZO~IU~I SALTS
p-diazo-o-chloro-N-diethylaniline
p-diazo-N-diethyl-m-phentidine
4-diazomorpholino-2J5-dibutoxybenzene
4-diazo-N-benzoyl-2,5-dibutoxyaniline
2-diazo-L,-napthol-5-sulfonic acid
p-diazo-diphenvlaminesulfate
4-diazo-(4'-toluyl)-mercapto-2,5-diethoxybenzene
Azo couplers for diazonium salts are well ~nown and include
phenols, napthols, and amincs. Particularly erfective azo couplers for the
foregoing diazonium salts include one or more of the following compounds:
AZO COUPLERS
2,7-dihylroxy-~,6-naphthalcnedisodiumsulfonate
beta oxynapthoic-monocthanolamidc
beta oxynapthoic-aminocthyleneamide-hydrocllloride
resorcinol
-- 6 --
m-hydroxyphenylurea
6,7-dihydroxy-2-naphthalenesodiumsulfonate
phloroglucinal
As set forth above, the coupler or diazonium saits may be varied
by the use of different couplers. For e~ampleJ p-diazo-o-chloro-N-diethylani-
line coupled with 2,7-dihydroxy-3,6-naphthalenedisodiumsolfonate ~orms a
sepia color while the s~ne diazonium salt coupled with beta oxynapthoic-aminoe-
thyleneamide-hydrochloride forms a brown color. Similarly, p-diazo-diphenyl--
aminesulfate coupled with $,7-dihydro~v-2-napi~thalenesodiumsulfonate forms a
blue color while the same diazonium salt coupled with resorcinol forms a
yellow cr.10r. In another example, 4-diazo-~4!-toluyl)-mercapto-2,5-diethyoxy-
ben~ene and phloroglucinol forms a black color while 4-diazo(4'-toluyl)-mercapto-
2,5-diethoxybenzene and resorcinal forms a red color.
One of the advantages of the ability to form different colors with
a single diazonium salt and a variety of azo couplers is in the flexibility o~
the laboratcry technician to dye a variety of lenses with different colors on
short notice. A few diazonium salts may be employed on the shelf of the tech-
nician together with appropriate a~o couplers to form a large variety of colors.
In the indicated form, the reagents are relatively stable.
Other methods may be employed for forming the desi~ed image.
Two of these methods described herein involve the use of an aqueous gel relief
for transferring the desired image and so will be designated as the "first
relief method" and "second relief method", respectively. They are particular'y
applicable for the formation of a relatively small image with a sharp border.
One use for thcse techniques would be to apply a colored coded symbol 0l1 the
lens as for thc dcsignation of the lens power.
In the first relief method~ an aqueous solution of a dia~onium
-- 7 --
71~9
salt of ~hc foregoing type is dispersed and absorbed by an aqueous gel relief
portion of an ilnaging substrate. Tho relief portion is contacted with the
lens to tr~nsfer the dia~onium salt to th~ lens. Flnally, the lens is con-
tacted with the a~o coupler for development.
The imagiilg substrate and gel relief portion nn~y be formed by any
conventional technique. For example, a solution of a gel precursor prior to
setting may be deposited in a mold wllich includes a relief in the form of a
negative image of the desired configuration. Then, the gel is permitted to
set. Any of a variety of gels, e.g., gelatin or cross-linked starch, may be
employed for this purpose.
The colored image may take the form of coded symbols such as let-
ters or numbers. To form the gel relief image, a ~old such as formed of plas-
er of paris may be constructed by solidification of the plaster in contact
with typeface. Then, the gel precursor is flowed into the mold and permitted
to set.
Other forms of gel relief may also be employed for special pur-
poses. For exa~ple, photo-derived reliefs may be employed such as used in
the photo-engraving industry.
For example, the film positive may be made of a desired coded
symbol such as a number of letter. Then, such film positive is contacted
with a photomechanical film including a gelatin surface ~ith silver salt dis-
persed therein on a plastic film backing ~e.g., Mylar). Thereafter, such
photomechanical film is developed to form a negative image area in which the
silver is in free form surrounding the positive image of the symbol in clear
gelatin form. Thereafter, the gelatin in the area of the negative image is
ren~ovcd by contact with a solution which attacks only the free silver-con-
taining black portion. A suitable solution for this purpose includes nascent
Trademark
-- 8 --
g
ox~gen produced by an aqueous solution of copper sulfate, nltric acid, potas-
sium bromide, and hydrogen peroxide. Then~ the dissolved negative image is
removed leavin~ a relief of the clear gelatin positive of the desired symbol
on a plastic film base. Typically, such a relief is a very thin film (e.g.,
0.01 - 0.05 mm thick) with precisely defined borders.
The gel relief portion may be molded onto a non-gel backing, if
desired. If the images are of a substantial size, it is preferable to form
*he gel relief of a material which is sufficiently flexible to conform to the
contour of the lens.
After the gel relief is soaked with diazonium salt, it is contacted
with the lens for a sufficient time, e.g., one minute or more, for the diazo-
nium salt to permeate and disperse into the lens to form an image of the
relief portion.
Then, the latent image on the lens is developed by contact with an
aqueous solution of an azo coupler of the foregoing type. This step is per-
formed by soaking with the azo coupler for a sufficient time for it to permeate
; the latent image area and coupl0 with the diazonium salt dispersed therein.
This coupling step is quite rapid and may possibly be accomplished by wiping thesu~face with a cloth soaked with azo coupler. After development, the foregoing
steps of washing and boilin~ in saline solution are performed.
It is believed that azo couplers are more compatible with the sal--
ine solution than are the diazonium salts. Thus, it may be advantageous to
reverse the order of addition of the diazonium salt and azo coupler in the firstrelief method. For e~ample, the azo cou~ler would be dispersed in an aqueous
solution into the gel relief portion of the imaging substrate and contacted Wit]the len~s to impart a latent image. Thcn, the latent image would be developcd
by contact with a diazonium salt. This may be accomplisiled rapidly as by wiping _ 9 _
~7~L~39
the surface of the lens and latent image arca with a cloth soaked with diazon-
ium salt.
Prior to contacting the soft lens with the diazonium salt solution
for eithcr the photomask or relief methods, it is preferable to hydrate the
lens in distilled water in contrast to concentrated saline solution. ~his is
because the salt of a conventional saline solution may interfere with the per-
meation of the diazonium salt solution. The diazonium salt may permeate the
lens if sufficient salt is leached first from the lens.
In the second relief method, an aqueous azo dye solution is pre-
formed which includes a diazonium salt, an azo couplerJ and a coupling inhibi-
tor (a pH reducing agent~. This solution is soaked into a gel relief of the
foregoing type and contacted with the soft lens to form the latent image. A
suitable pH reducing agent comprising a food grade acid such as citric acid.
Citric acid is advantageous in that it can be stored in a solid crystal form
for indefinite periods. Also, the diazonium salt and azo couplers may be
stored in solid form. Thus, all ingredients of the latent dye solution may
be stored for an indefinite period of time in a solid form tmtil just prior
to use. Thenl the solids may be mixed into water to form the latent dye
~- solution.
The pH reducing agent serves as a coupling inhibitor because of the
well known phenomenon that coupling does not occur at low pH levels. In the
absence of this inhibitor, coupling would occur in a matter of minutes. This
would necessitate constant mixing of individual solutionsJ a time consuming
procedure. It has been found that in the presence of sufficient acid to lower
the pH level of the otherwise neutral mixture to say about 5.5 - 6.5, the
latent dye solution is stable for storage times on the order of as long as one
to two weeks.
- 10 -
7~L9~
The foregoing latent azo dye solution is soaked into a Eel relief
as described above for a sufficient time for absorbtion into the gel. A
suitab]e time for this purpose is from one to five minutes.
The soaked gel relief is then contacted with a soft contact lens
to form a latent image. This is a very rapid process and may be accomplished
in about one to five seconds. Thereafter~ the latent image is developed by
increasing the pH level in its area of the contact lens to a sufficient extent
to promote coupling. A pH level on the order of 7.S - 8.5 is generally suit-
able for this purpose.
A unique technique for increasing the pH level of the lens for
development while avoiding extensive contact of the lens with a potentially
harmful basic solution is to expose the lens to a basic gas. For example,
exposure to ammonia ~as produced by a weak ammonia aqueous solution leads to
a very rapid development of the image. Soaking the lens in a basic solution
could be practiced as a less desirable alternative.
One advantage of the second relief method is that only a minute
portion of the lens in the form of the coded symbol is contacted with dye
solution. This is desirable from a health standpoint. In addition, potential
harmful expansion or attack of the lens by a basic solution is avoided by the
useOf the gas for~ of the base.
Ater development, the foregoing steps of washing and boiling in
saline solution are performed.
It is apparent that the foregoing relief metho~s are of particular
advantage where the image is relatively small and a precise boundary is desired
for the colorcd image. Thus, such methods may be employed for coding with
numbcrs or letters. This may be accomplished with a series of spaced rclief
images soaked with appropriate dia~onium salt for the rapid coding of such
39
lenses. For example, a wheel with a strip of flexible non-slip gel relief
images may be used.
Referring to the drawingsJ an apparatus is prov:ided for precisely
depositing an imaging liquid on~o a limited area of a contact lens. Such
imaging liquid could include either the diazonium salts or azo couplers of the
first relief method or the latent dye solut~n of the second relief method.
In any event, the apparatus provides means for precisely contacting a limited
area of the contact lens with the desired symbol provided in a relief layer to
form a crisp image.
Referring specifically to the embodiment of Figures 2 and 3, a device
11 is illustrated for rapidly imprinting one or more contact lenses with the
same or different symbols. Device 11 includes a platform 12 to ~hich is
mounted means 13 for supporting the sof~ contac~ lens. Such means includes
vertical suppor-t base 14 which threadedly receives an adjustment scre~ 16.
Body 17 is mounted for adjustable pivotal movement to screw 16 and includes a
projecting convex surface 18 contained to firmly support the soft contact lens
illustrated by dotted lines 19. By adjustable mounting in this manner) the
portion of the lens to be contacted and the level of the lens wi~h respect to
the striker arm described hereinafter may be adjusted to the desired extent.
A vertical support member 20 is mounted to platform 13 and carries
a plurality of striker arms each including a relief layer as described herein-
after. A rotatable striker arm mounting means 21 includes a central shaft 22
carriedby an openinginsupport member 20 with removable gripping knob 23 a~ one
side of membcr 20 and a striker arm support body 24 carried at the other side
of membcr 20. ~ody 2~ is of square cross-section and includes four flat
mounting surfaces 24a - 24d for providing multiple support areas for striker
arms carried by the support body at 90~ angles to each othcr. hlore surfaces
- 12 -
may be provided for more striker arms as desired.
Striking means is provided including a movable striker arm 26
illustratcd in expanded view in ~igure 1. Arm 26 includes mounting openings
27 for riveting to each of respective surfaces 24a - 24d. In the embodiments
of ~igures 2 and 3, the striker arms mounted ~o surfaces 24a - 24d will be
designatcd 26a - 26d, respectively. The individual striker arms include a
minute imaging liquid absorptive relief layer 28 at the free end of the arm.
Such relief layer may be formed in the manner set forth above.
Stiker arm 26 is preferably formed as a resilient strip of a trans-
parent plastic material such as the polyester ilm sold under the trademark
"Mylar". Other resilient materials also may be employed.
Support body 24 is rotatable by knob 23 ~o move the free ends ofany of striker arms 2~a-2~d into a position adjacent to convex surface 18 to
permit striking of the same with the symbol of relief layer 28, mounted to face
exterior support body 24. In the embodiment of Figures 2 and 3, arm 26c is in
a horizontal position ready for striking. In this position, the striker arm
is movable between the i`llustrated normal position spaced apart from surface
18 and a striking position in which the relief layer is pressed against a
limited area of contact lens 19 on surface 18. The actual striking motion
~0 actuation may be accomplished by manually pressing arm 26a against the lens for
a short period of time. Alternatively, remote means may be provided for actu-
ation. In any event, the overall apparatus serves to accomplish this objective
in a precise manner.
It is apparent that different symbols may be employed for each of
the relief layers on the different striker arms to employ different codes for
a succession of lenses placed on convex surface 18. In this manner~ for ex
ample, a code for the prescription of different lenses ma~ be printed on a
- 13 -
~1~7~
rapid succession of lenses. It is apparent that each striker arm is horizon-
tally positioned to strike a succession of contact lenses ~ convex surface 18
at mutually exclusive times during rotation of the mounting means.
Coding means is operatively associated with each striker arm in
the form of enlarged symbols corresponding to the respecti~e images on ~he
relif layer imaging surfaces. Such images are illustrated by the figure 8 in
Figure 1. It is desirable because the relief layers 28 are so small as to not
be readily visible to the naked eye. Thus, this provides a safety measure
to assure that the proper image is imprinted on the lens.
A table 29 is provided with a visible line on its generally hori-
zontal top surface for registry with the corresponding line 30 of the striker
arm as an indication that relief layer 28 is precisely aligned for proper im-
printing onto the lens. Alternatively, this system could be performed by ap-
propriate stops in the rotation of support body 24. However, alignment as
illustrated herein is a very economlcal manner o accomplishing this objective.
Support body 24 is removable from member 20 by disengaging knob 23
and sliding the body ~n the opposite direction. Thus, the relief layer con-
taining portions of all striker arms may be soaked simultaneously in a dye
solution. Also, if desired, another body with previously soaked striker arms
may be used in the apparatus during tllis time.
Soft contact lenses colored by the foregoing techni.ques may be
employed for a number of different purposes. For example, a transparent con-
t-act lens with a central opaque portion may be employed to occlude the retina
of the eye to treat a patient with amblyopia. Also, ~he colored portion of the
contact lenc co~ld be used as a ~ilter to replace sun glasses, e.g., as a ski
lens. Furthermore, the lells may bc e~ployed for various cosmctic reasonss-lcl
as changing the color of the wearer's iris or even to provide colored images
- 14 -
~7~9
such as stars or lines radiating from the iris, in the white portion of the
we~rerls eyes.
A further disclosure of the nature of the present inventionis pro-
vid~d by the following specific examples of the practice of the same. It should
be understood that the data disclosed serve only 2S examples and are not in-
tende~ to limit the scope of the inv~ntion.
Exam~le 1
The following is a description o~ ~he photomask method. The lens
;~ is first immersed in a solution of p-diazo-o-chloro-N-diethylan~line at a con-
centration of 0.1 gram of salt in 4 ounces or dislilled waler Coa~L~
0.025% hydrochloric acid. The lens is immersed at 75~F for 45 minutes.
After the immersion step, the lens is disposed one foot from a
100 ~Yatt mercury vapor lamp. A photomask is positioned intermediate the lens
and lamp upon which an image in black of the desired configuration is posi-
tioned on a transparent base. This image is in the form of the iris of the
eye. Then, the lamp is activated for an exposure time of g minutes to de-
compose the diazonium salt in the exposed areas so that it will not form a
color when developed.
After exposure, the lens is soaked in a solution of an azo coupler
color developer comprising 2,7-dihydroxy-3,6-naphthalenedisodiumsulfonate
at a concentration of 0.1 gram in 4 ounces of t~ater. 3 cc of this solution is
comblncd with 1 cc of a dilute sodium carbonate solution formed from 1 gram of
sodium carbonate dissolved in 1 liter of water. The time of immersion is
about 5 minutes during which a sepia color is developed. After development,
the lens is washed in distillcd water and boiled in normal saline solution.
The color formed in the image area is insoluble in water and is distributed
throughout thc thickness of the lens.
- 15 -
~71~9
Example 2
The procedure o~ Examplc i is followed with the exception that
the coupler is formed of beta oxynapthoic aminoethyleneamide-hydrochloride.
A brown color is formed in the image area.
Example 3
The procedure of Example l is followed with the exception that
p-diazo-diphenylaminesulfate is subst.ituted for p-dia~o-o-chloro-N-diethy-
laniline and 6,7-dihydroxy-2-naphthalenesodiumsulfonate is substituted for
2,7-dihydroxy-3,6-naphthalenedisodiumsulfonate. A blue color is formed.
Example 4
The procedure of Example 3 is followed with the exception that
resorcinol is substituted for 6,7-dihydroxy-2-naphthalenesodiumsulfonate. A
yellow color is formed.
Example 5
The procedure of Example I is followed with the exception that
4-diazo-(4'-toluyl~-mercapto-2,5-diethoxybenzene is substituted for p-diazo-
o-chloro-N-diethylaniline and phloroglucinol is substituted for 2,7-dihydroxy-
3,6-naphthalenedisodiumsulfonate. A black color is formed
Example 6
The procedure of Example 5 is followed with the exception that
resorcinol is substituted for phloroglucinol. A red color is formed.
Example 7
- The following procedure is an example forming a ~isible image on
the soft contact lens by the second relief method. The aqueous latent azo dye
solution is formed by mixing the following ingredients in dry powder form into
8 ounccs of distilled water:
- 16 -
0.6 grams of p-diazo-N-diethyl-M-phenetidinc zinc chloride
0.6 grams of p-diphenylamine sulfate
0.2 grams of citric acid crystals
0.5 grams of 6,7-dihydroxy-2-naph-thalene sodium sulfonate
A film including a relief of the coded symbol is dipped into the
solution for a sufficient time to permit absorption of the solution into the
gel relief. Then, the symbol is rapidly contacted with the soft lens to im-
part a latent image to the same. Finally, the lens is exposed to weak ammonia
vapors for several seconds to develop the image into a permanent blue color.
Thereafter, the lens is washea in distilled water and boiled in normal
saline solution.
- 17 -
.
