Slow-drying aqueous-based coating materials and painting techniques for the use thereof

Products are disclosed to be applied to a given surface to be painted in which the drying time of the product on the coated surface is delayed so as to increase the useable working time for the painting surface. The base coating products consist generally of mixtures of synthetic resin water-based paints preferably acrylic colorless or colored paints, glycerin USP 96% and water in predetermined ratios by weight. The synthetic resin water-based paint as an ingredient when colorless provides a colorless base coating composition and, when colored, provides a colored base coating composition. The enumerated coating compositions may also include, in predetermined ratios, small quantities of surfactants and/or thickening agents which enhance the purpose and object of the enumerated coating compositions for delaying the drying time so as to increase the time during which the coated surface can be worked by applying, blending and overcoating the base coated surface with synthetic resin water base paints. Also illustrated is a method or process of "wet on wet" painting technique consisting of formulating the particular base coating compositions desired, coating this particular base coating composition on at least one a portion of the given painting surface and creating and overcoating the base coated painting surface by applying and working water-based paints so long as the base coated painting surface remains wet and workable. Additionally, a painted surface with a base coating composition as the undercoating and an applied overcoating thereon consisting of synthetic resin acrylic paints. Additionally, an emollient to be mixed or stirred with a synthetic resin acrylic or water-based paint in relatively small quantities before using the paint, to delay the drying time thereof, has as its principal ingredient a humectant preferably glycerin USP 96%.

This invention relates generally to slow-drying aqueous or water-based 
coatings and paints and more particularly to slow-drying aqueous-based 
coating compositions including synthetic resin acrylic paints and the use 
of such compositions for improved "wet on wet" painting techniques. 
BACKGROUND OF THE INVENTION 
When used herein, "wet on wet" refers to a painting technique in which the 
drying times of the coating compositions and/or the paints applied to a 
canvas or other surface being painted or on which an artist is working to 
create a painting are delayed so as to extend the time during which the 
surface can be satisfactorily and creatively worked to obtain the result 
desired by the painter or artist. 
Heretofore this technique has only been used successfully by artists using 
oil-based coating compositions and paints. This, however, has limitations 
because oil-based coating compositions and paints, particularly when used 
indoors, have strong and sometimes unpleasant odors and additionally are 
hazardous because of the solvents used in such oil-based coating 
compositions and paints. 
Aqueous or water-based coating compositions or paints for use in such "wet 
on wet" painting techniques present difficulties because of their rapid 
drying characteristics coupled with the normal formation of a film or skin 
on the composition after it is coated on a surface, particularly where the 
coating has a thickness such that the film dries while the undercoating 
remains liquid or wet. Those skilled in the art will recognize that the 
drying of such aqueous or water-based paints occurs because of a phase 
reversal from liquid to solid of the applied coating material upon loss of 
water in the composition generally by evaporation and the agglomeration of 
the polymer particles of the water-based composition into a coherent film. 
In the case of a thicker coating of the water-based composition, this 
occurs first at the surface. This phase change from a continuous water 
phase to a continuous solid phase is a physical reaction which is 
generally irreversible. Therefore, it impedes the ability to further work 
the surface to which such paint compositions have been applied. 
Slow-drying water-based coating compositions are known, such as is shown 
and disclosed in U.S. Pat. No. 3,374,196. In this patent a wide variety of 
water-based natural rubber latex coating compositions are identified and 
the difficulties due to rapid drying and skin formation due to the 
thickness of the latex compositions when applied to a surface are overcome 
by additives to the latex compositions that retard the rate of drying and 
of skin formation. The particular additive identified is a combination 
obtained from a physical mixture of urea and a non-polymeric water soluble 
glycol, such as glycerin, ethylene glycol or sorbitol. When this additive 
is combined with the latex compositions in the manner disclosed, a 
paste-like latex composition is formed which has the same rheological 
properties as conventional artists' oil paints. A preferred additive 
mixture consists of one part by weight of urea and one part by weight of 
glycerin formed by heating the glycerin to 250.degree. F. and dissolving 
the urea therein, in the form of urea pills, until the urea is fully 
dissolved. This specific additive delays the drying time of the paste-like 
natural rubber latex composition to which it is added but only about 
twenty (20) minutes. 
Pat. '196 makes it clear that there is some synergistic effect between the 
urea and the glycerin for delaying drying time of the natural rubber latex 
composition vehicle to which they are added because this patent 
specifically states that such delay in drying time cannot be achieved by 
either of these ingredients separately. The same effect was found to apply 
for other normal humectants such as ethylene glycol, propylene glycol and 
the like. 
In the present invention, contrary to U.S. Pat. No. 3,374,196, it has been 
found that by adjusting the ratio of glycerin, or the ratio of glycerin 
and other additives to a synthetic resin water-based composition such as 
an acrylic paint or coating material, results in the formation of a 
synthetic resin acrylic composition with material and substantial delays 
in the drying time of such synthetic resin water-based or acrylic 
compositions to the extent that when such improved synthetic resin acrylic 
compositions are coated on and worked into a surface on which a painting 
is being made, these substantial delays in drying time of the coating 
applied to the surface extend the working time for water-based paints 
overcoated onto the base coated surface and thus enable the painter or 
artist to achieve advantages or necessary painting changes and finishes on 
the coated surface. In this regard, not only is it possible to provide 
synthetic resin water-based acrylic coating compositions, but also 
improved paste-like synthetic resin water-based acrylic compositions, each 
with their respective delay in drying time for achieving these 
advantageous results and characteristics. However, these respective delays 
in drying time, as will be clear from the examples set forth hereinafter, 
are at least in the order of forty (40) hours or more and thus provide 
extended working time for overcoating the base coated surface being 
painted. Thus, these synthetic resin acrylic coating compositions serve 
well as undercoatings and are adapted to be used synergistically with 
either regular commercial acrylic paints or with the improved synthetic 
rubber paste-like acrylic compositions in accordance with the present 
invention to meet the requirements for use in "wet on wet" painting 
techniques by artists, particularly those who wish to paint indoors as 
well as elsewhere. 
Acrylic, when used herein, is a designation for a series of colorless 
olefin pungent acids obtained from the oxidation of acrolein having the 
general formula C.sub.n H.sub.2N O.sub.2. 
Acrylic paints or coating compositions are any of a group of thermoplastic 
synthetic resins formed by polymerizing esters of acrylic acid or 
methylacrylic acid. These materials are different and distinguishable from 
alkyd resins and natural rubber latex materials. 
Any acrylic materials as above identified may be used in the formation of 
the improved acrylic compositions in accordance with the present 
invention. Such acrylic materials and other ingredients of these improved 
formulations are purchasable in the commercial marketplace or are readily 
available. These ingredients for such improved formulations may consist of 
one or more of the following: 
Pebeo.TM. Acrylic Clear Paint 
Pebeo.TM. Acrylic White Paint, Extra Fine Color 118 Series 1, Blanc de 
Titane 
A humectant such as Glycerin USP 96% which has an affinity for water with 
stabilizing action on the water content of a material and keeps the 
moisture content caused by humidity within a narrow range 
Acrylic Flow Improver--a concentrated solution of wetting agent 
Pebeo.TM. Acrylic Gel--a thickening agent 
These may be used and mixed in the improved formulations of the acrylic 
compositions in accordance with the present invention in ratios either by 
volume or by weight. 
Thus, the general steps for the formulation of the aqueous coating 
compositions or paint formulations, to provide a better understanding of 
the invention, will now be illustrated by reference to the following 
examples.

EXAMPLE 1 
In early afternoon at an ambient temperature of 70.degree. F. and relative 
humidity of 50%, full-strength glycerin was coated on the surface of a 
canvas, and the surface of the canvas was checked for wetness every hour 
after the surface was coated. After fourteen (14) hours the surface of the 
canvas was still wet; however, the appearance of the surface was blotchy, 
streaky and pebbly-looking. While the full-strength coating with just 
glycerin kept the surface of the canvas wet, the performance as an 
undercoating for the "wet on wet" painting technique was rated as poor. 
EXAMPLE 2 
In early afternoon at an ambient temperature of 70.degree. F. and relative 
humidity of 50%, an acrylic composition consisting of: 
81/2 oz. or 11/2 parts by volume of acrylic white, 
91/2 oz. or 11/2 parts by volume of glycerin and 
33/4 oz. or 3/4 parts by volume of tap water was mixed together, stirred 
and shaken well for a period of at least three (3) minutes. 
This mixture was applied by a brush and worked into a canvas to provide a 
white coating base on the surface of the canvas. Using the "wet on wet" 
painting technique, a portion of this white base coated surface on the 
canvas was overpainted with conventional acrylic colored paints. These 
paints were applied and blended well onto the wet acrylic white base 
coated on the surface of the canvas. The remaining portion of the white 
base coating on the surface of the canvas was checked hourly, and over 
forty (40) hours after the white base coating had been applied, this 
remaining portion of the coated surface of the canvas was still wet. 
Thus, this mixture achieved the purpose and objects of the present 
invention for "wet on wet" painting techniques. 
EXAMPLE 3 
In early afternoon at an ambient temperature of 70.degree. F. and humidity 
of 50%, an acrylic composition consisting of: 
2 oz. of Pebeo.TM. Acrylic Clear, 
10 oz. of glycerin and 
6 oz. of tap water was mixed together, stirred and shaken well for a period 
of at least three (3) minutes. 
This clear coating mixture was applied by brush and worked into the surface 
of a canvas. The coated base composition on the surface of the canvas 
material was checked every hour after it was coated. After forty (40) 
hours the coating on the canvas was still wet. The appearance of the 
mixture coated on the surface of the canvas had a smooth and even texture. 
This mixture has the properties for excellent performance for use in the 
"wet on wet" painting technique. 
EXAMPLE 4 
In late afternoon at an ambient temperature of 70.degree. F. and relative 
humidity of 60%, an acrylic composition consisting of: 
2 oz. of Pebeo.TM. Acrylic Clear, 
12 oz. of glycerin and 
4 oz. of tap water 
was mixed, stirred and shaken together for about three (3) minutes. 
This mixture was brushed onto the surface of a canvas and provided a clear 
base coated surface on the canvas. The coated surface on the canvas was 
checked every hour after it was coated. During the same time frame a 
portion of the coated surface on the canvas was overpainted with 
conventional acrylic paints. The colors of the acrylics used for 
overpainting applied well and blended well, which could not be done to the 
canvas without the base undercoating of this acrylic composition mixture. 
After some sixty (60) hours, a check of the portion of the coated canvas 
which had not been overpainted was still wet, and the appearance of the 
coated composition had a smooth even texture, but fuller in appearance 
than the composition of EXAMPLE 3. The performance for "wet on wet" 
painting technique was only fair. 
EXAMPLE 5 
In late afternoon at an ambient temperature of 70.degree. F. and relative 
humidity of 60%, an acrylic composition consisting of: 
2 oz. of Pebeo.TM. Acrylic White, 
10 oz. of glycerin and 
4 oz. of tap water 
was mixed and stirred together for about three (3) minutes. 
This mixture was brushed onto the surface of a canvas and provided a white 
base coating on the surface of the canvas; the coated surface of the 
canvas was checked every hour after it was coated. During this same time 
frame a portion of the canvas that had been coated was overpainted with 
conventional acrylic paints. The colors of the acrylics used for 
overpainting applied and blended well, which could not be done to the 
canvas without the base undercoating of this acrylic composition mixture. 
After some sixty (60) hours, a check of the portion of the coated canvas 
which had not been overpainted was still wet, and the appearance of the 
surface with this white base coated composition had a smooth even texture, 
although the coating had some lumps; nonetheless, it served well for 
painting in accordance with the "wet on wet" painting technique. The 
performance for "wet on wet" was good but a smoother mixture was needed 
such as the mixture provided by EXAMPLE 3. 
EXAMPLE 6 
In the late afternoon at an ambient temperature of 70.degree. F. and 
relative humidity of 50%, an acrylic composition of: 
2 oz. of tap water and 2 drops (minims) of Acrylic Flow Improver 
(concentrated wetting agent) were mixed, stirred and shaken for one (1) 
minute; 
1 oz. of Pebeo.TM. Acrylic White was added, and this mixture was then 
stirred and shaken for about one (1) minute; then 
5 oz. of glycerin was added to this second mixture, stirred and shaken for 
about one (1) minute. 
This mixture was then brushed and worked into a portion of a canvas to 
provide a white base coating on the surface of the canvas. Shortly 
thereafter, portions of this coated surface of the canvas was painted with 
conventional orange-colored, yellow-colored, white-colored and 
blue-colored acrylic paints. These paints blended well into the coated 
surface of the canvas. The unpainted undercoating on the canvas was 
checked hourly, and forty (40) hours after the canvas had been coated, the 
coating was still wet. The performance for "wet on wet" painting with 
water-based paints was good. 
EXAMPLE 7 
In the late afternoon at an ambient temperature of 70.degree. F. and 
relative humidity of 50%, an acrylic composition of: 
1 oz. of tap water and 2 drops (minims) of Acrylic Flow Improver 
(concentrated wetting agent) were mixed, stirred and shaken for one (1) 
minute; 
1 oz. of Pebeo.TM. Acrylic White was added, and this mixture was then 
stirred and shaken for about one (1) minute; and 
1/2 oz. of Acrylic Gel was added to this second mixture, then stirred and 
shaken for about one (1) minute; then 
11/2 oz. of glycerin was added to this third mixture, stirred and shaken 
for about one (1) minute. 
This mixture thus formulated was then brushed and worked into a canvas to 
provide a white base coating on the surface of the canvas. Two (2) hours 
after the canvas had been coated, the base coating was still wet. 
Thereafter, portions of this coated surface of the canvas was painted with 
conventional orange-colored, yellow-colored, white-colored and 
blue-colored acrylic paints. These paints blended well into the coated 
surface of the canvas. The unpainted undercoating on the canvas was 
checked hourly, and after sixty (60) hours, this base coating on the 
surface of the canvas with the mixture as above formulated was still wet. 
The performance for "wet on wet" painting with water-based acrylic paints 
was considered excellent. 
EXAMPLE 8 
In the late afternoon at an ambient temperature of 70.degree. F. and 
relative humidity of 50%, an acrylic composition of: 
2 oz. of tap water and 2 drops (minims) of Acrylic Flow Improver 
(concentrated wetting agent) were mixed, stirred and shaken for one (1) 
minute; 
2 oz. of Pebeo.TM. Acrylic White was added, and this mixture was then 
stirred and shaken for about one (1) minute; then 
2 oz. of glycerin was added to this second mixture, stirred and shaken for 
about one (1) minute thereafter; 
2 oz. of Pebeo.TM. Acrylic Gel was added to this third mixture, stirred and 
shaken for about one (1) minute. 
This mixture was then brushed and worked into a portion of a canvas to 
provide a white base coating on the surface of the canvas. Shortly 
thereafter portions of this base coating on the canvas was painted with 
conventional orange-colored, yellow-colored, white-colored and 
blue-colored acrylic paints. These paints blended well into the coated 
surface of the canvas. Approximately one (1) hour after the canvas had 
been coated with the mixture as above formulated, I overpainted the canvas 
with a seascape wing white, blue, yellow, orange, pink, paynes grey, brown 
and black conventional acrylic colored paints. The colors blended well, 
the mixture was smooth, and the performance for "wet on wet" painting was 
excellent. 
The unpainted portions of the undercoating on the canvas was checked hourly 
and was still wet over seventy-two (72) hours after the canvas had been 
coated. 
EXAMPLE 9 
In the late afternoon at an ambient temperature of 70.degree. F. and 
relative humidity of 50%, an acrylic composition of: 
4 oz. of tap water and 2 drops (minims) of Acrylic Flow Improver 
(concentrated wetting agent) were mixed, stirred and shaken for one (1) 
minute; 
4 oz. of Pebeo.TM. Acrylic White was added, and this mixture was then 
stirred and shaken for about one (1) minute; then 
6 oz. of glycerin was added to this second mixture, stirred and shaken for 
about one (1) minute thereafter; 
1/2 oz. of Pebeo.TM. Acrylic Gel was added to this third mixture, stirred 
and shaken for about one (1) minute. 
This mixture was then brushed and worked into a portion of a canvas to 
provide a white base coating on the surface of the canvas. Shortly 
thereafter portions of this base coating on the canvas was painted with 
conventional orange-colored, yellow-colored, white-colored and 
blue-colored acrylic paints. These paints blended well into the coated 
surface of the canvas. Approximately one (1) hour after the canvas had 
been coated with the mixture as above formulated, I overpainted the canvas 
with a seascape wing white, blue, yellow, orange, pink, paynes grey, brown 
and black conventional acrylic colored paints. The colors blended well, 
the mixture was smooth, and the performance for "wet on wet" painting was 
excellent. 
The unpainted portions of the undercoating on the canvas was checked hourly 
and was still wet over sixty (60) hours after the canvas had been coated. 
From the above examples certain conclusions can be drawn. First, a base 
coating of 100% standard USP glycerin will maintain the surface to be 
painted wet for many hours but will not serve as a base coating for the 
"wet on wet" painting technique because it does not have the appearance or 
the texture needed to apply and blend conventional acrylic colored paints 
to such glycerin coated surface. Second, a good composition to provide a 
clear base undercoating on a surface to be painted can be formulated from 
Pebeo.TM. acrylic clear, glycerin and tap water wherein the optimum 
mixture of these ingredients is in a ratio of 11 to 55 to 33 by weight. 
This ratio can be varied to also provide good mixtures for this purpose by 
adjusting the ratio of glycerin between 62 and 55 by weight with tap water 
between 37 and 33 by weight. Third, a good composition to provide a 
colored base undercoating on a surface to be painted can be formulated 
from Pebeo.TM. acrylic white, glycerin and tap water where the optimum 
mixture of these ingredients is in a ratio of 27 to 41 to 27 by weight. As 
in the clear base undercoating mixture, these ingredients can be varied by 
adjusting the ratio of the glycerin and the tap water. Fourth, the mixture 
can be further enhanced to delay drying and to increase working time for 
the application of acrylic colored paints by adding small quantities of 
wetting agents and/or thickening agents to the above defined ratios of 
these mixtures. These variations can also serve as a means for formulating 
acrylic paints which have delayed drying time. Thus, in accordance with 
the present invention many synthetic resin water-based compositions are 
capable of formulation which can be used synergistically with the mixtures 
defined above for the base coatings on a surface to be painted without 
departing from the scope of the present invention. 
Further, it is noted that the examples show that the various illustrated 
synthetic resin base coating compositions were brushed into or on the 
surfaces being coated. This technique was used as the preferred method in 
these examples in order to limit the thickness of the base coating applied 
to the surface to be overcoated with further synthetic resin water-based 
paints and thus to avoid the film or skin drying effect on the surface of 
the base coat to defeat the object and purpose of the present invention 
namely to delay the drying of the base coating on the surface being 
painted so that the coated surface remains wet and can be worked by the 
painter or artist a substantial period of time to modify and achieve 
greater creativity. 
To illustrate such limitations on film or skin formation, it was 
established that a gallon of any of the variations of base compositions 
illustrated in the above examples will cover 450 sq. ft. or 0.28444 of an 
ounce per square foot. Thus, on a canvas or other surface to be painted of 
16" by 20" which is 2.1875 sq. ft. the total weight of the applied base 
coating composition will be 0.6222 of an ounce. Thus, one type of an 
uncoated 16".times.20" canvas surface was measured and found to weigh 17 
ounces. When this canvas surface was coated, it weighed 18.25 ounces wet. 
After drying the canvas weighed 17.64 ounces. Thus the weight of the 
coating was 0.29257 ounces per sq. ft. A coating with this weight per 
square foot provided a thickness to the base coatings in a range from 1/2 
mil to approximately 2 mils and a preferred range of 1/2 mil to 1 mil. 
This weight and range of thickness prevented the film or skin drying 
effect from occurring on the base coatings applied to a given surface 
being painted and thus did not interfere with the delay in drying time of 
any base coatings applied to a surface to be painted. 
Accordingly, the quantities of paint, humectant and water must be selected 
to obtain a viscosity effective to provide a coating of this desired 
thickness. This can be determined by one of ordinary skill in the art 
without. undue experimentation. 
Thus synthetic resin water-based compositions have been illustrated which 
overcome the problems of the prior art regarding the adverse effect of 
odors, solvents and the formation of dry films or skins particularly 
adapted for use in "WET on WET" painting techniques for synthetic resin 
water-based paints as will now be further described. 
"WET ON WET" PAINTING TECHNIQUE FOR SYNTHETIC RESIN WATER-BASED PAINTS 
In using any of these water-based coating compositions to achieve the 
desired "wet on wet" painting technique, the canvas or other surface being 
painted is first preferably completely coated with either, or a 
combination of either, the clear form of the water-based coating 
composition or the colored form of the water-based coating composition in 
the approximate weight and thickness, all as above described and as may be 
required for the particular work being made or performed on the given 
surface being painted. 
After the canvas has been coated, the coated surface serves as an 
undercoating, and so long as the coated surface remains "wet", the painter 
or artist can apply either conventional paints or modified paste-like 
paint formulations as hereinafter described, and work and blend these 
overcoatings onto the coated surface of the canvas or other surface on 
which the painting is being performed. 
Modified Paste-Like Paint Formulations 
Conventional off-the-shelf Synthetic Resin Acrylic and other water-based 
paints having a drying time of about thirty (30) minutes or less depending 
on the film or skin formation, the ambient conditions and the nature of 
the surface being painted. This limits the usable working time of such 
paints. 
As another aspect of the present invention, it has been found that the 
working time of conventional off-the-shelf synthetic resin acrylic and 
water-based paints can be materially extended by delaying such drying time 
by adding thereto limited quantities of an emulsion having, as a basic 
ingredient, a humectant, preferably the glycerin USP 96%. When these 
off-the-shelf paints are so modified, they can be used directly on a given 
surface to be painted when only a short period of delay in the drying time 
of the applied paint is required or they can be applied and worked onto a 
surface to be painted having a base or undercoating of one or more of the 
base coating compositions, as are illustrated in the examples set forth 
above, where a greater delay in the drying time is desired or required by 
the painter or artist. 
EXAMPLE 10 
One such emulsion was made in the early evening at an ambient temperature 
of 70.degree. F. and relative humidity of 50% by hand mixing or stirring 
together on a palette: 
11/2 oz. of an off-the-shelf conventional acrylic green paint, and 
5 drops (minims) of glycerin USP 96% containing 0.01% by volume of a 
surfactant, sodium lauryl sulfate. 
This mixture was applied to a first section of a canvas painting surface 
having one of the base coating compositions as above described. The 
unmodified conventional off-the-shelf acrylic green paint was applied to a 
second section of this coated canvas painting surface. These respective 
sections of the coated canvas painting surface were monitored and checked 
from time to time for wetness. 
It was determined from the monitoring that the section of the coated 
painting canvas dried in about five (5) hours. It was further determined 
that the modified off-the-shelf acrylic green paint as above described 
over ten (10) hours and therefor had a working time or remained wet 
greater than 100% than the working or drying time of the conventional 
off-the-shelf acrylic green paint. 
Thus a still further means for controlling drying time for use in the wet 
on wet painting technique is provided with the use of such modified 
conventional off-the-shelf synthetic acrylic or water-based paints when 
applied to surfaces to be painted which are undercoated with one of the 
base coating combinations as described herein. 
Those skilled in the art will readily recognize that synthetic resin 
water-based paints or the like coating compositions having the same or 
similar composition to the acrylic paints identified in the examples may 
also achieve the same advantageous results, The present invention also 
contemplates the manufacture of synthetic resin water-based paint products 
for the commercial marketplace having extended or delayed drying time in 
which conventional off-the-shelf formulations are modified by the addition 
of quantities of water and humectant effective to at least double the 
drying time of such formulations. 
While only a few examples of synthetic resin water- or aqueous-based 
coating compositions or paint formulations are described above to 
illustrate the invention, it will be apparent that many different 
modifications and equivalents may be made without departing from the 
spirit and scope of the present invention. Therefore, the invention is not 
intended to be limited thereby, except as defined by the appended claims.