Ammonia-dissolved pre-vulcanized latex is of everyday usage to make flexible moulds and peelable protections. In this last case, it is mainly used in ceramic decoration, to carry out resists in the application of engobes, glazes or colourants.
The liquid latex solution is applied with a brush to the dry area to protect in less than 15 minutes, and then becomes rubbery. After application and drying of the layer of engobe, colourant or glaze, one withdraws the solidified latex film by gently separating it from the ceramic object with a pair of small pliers or a blade.
The elasticity of latex facilitates the unsticking and generally the pieces are withdrawn as a whole and in one time.Then the parts protected by latex appear free of engobe, colourant or glaze.
This technique is particularly
appreciated when products of very different colours must be
superimposed while being well delimited, or if the colour of the
ceramic object or shard must appear non-coloured in the case of
application by spraying or dipping.
Attention, if the porosity of the object
is too important the layer of latex will be difficult to withdraw.
Always make a test before launching out in a long work.
It is necessary to proceed in a well
ventilated room to avoid breathing ammonia vapor. In the case of a
daily and long use of this technique, it will be necessary to
consider means of suitable protection and ventilation.
Brushes must be washed between each
application and drying of latex.
Ammonia is used mainly in the
manufacture of fertilizers and of many other products in a very
large variety of fields. It is used as a cooling gas in the
industry of industrial refrigeration.
One can also find it as a cooling gas in
arenas, and as an air contaminant in breeding settings (examples:
Ammonia is also found as liquid ammonia
which is in fact gaseous ammonia dissolved in water (solution of
ammonia at 28% or ammonia at 28%).
Hygiene and Safety
Ammonia is a colourless gas with a
characteristic and prickly odor. It is a suffocating gas at high
Exposure to ammonia in the work
environment occurs mainly as a gas, because of its very low
boiling point and its great volatility. The exposure to liquified
ammonia generates a significant gas concentration because of its
very low boiling point and its high volatility.
The exposure to liquified ammonia is
increasingly frequent because of its use in refrigeration systems.
Moreover, concentrated aqueous ammonia solutions can emit ammonia
vapors at high levels of concentration.
III-Exposure to the gas :
The prickly odor characteristic of
ammonia can be detected at 16,7 ppm, which is in the same order of
magnitude as the VEMP, 25 ppm or 17 mg/m³; at a VECD of 35
ppm or 24 mg/m³; at an IDLH value of 300 ppm or 209
mg/m³ and at the lower limit of explosiveness at 13 % or 13
000 ppm; so that it can be a sign of adequate warning before the
exposure becomes dangerous.
An olfactive fatigue occurs following
repeated exposures, therefore the odor cannot be an adequate sign
of warning to an exposure exceeding the VEMP or the VECD. However,
the olfactive threshold is sufficiently low to prevent a situation
IV-Exposure to the liquid :
Ammonia is a liquid at -33,35°C. In
the liquid state, it is thus necessary to take into account all
the aspects which comprise the exposure to a liquid at low
Immediately dangerous to life or health
(IDLH) : 300 ppm
V-Inflammability and explosiveness :
The fire hazard caused by ammonia is
relatively low, it must be put in contact with materials or a
surface having a temperature of 651°C before igniting itself
However the presence of oil or other
combustible materials can increase the fire hazard by lowering
this temperature of autoignition. Ammonia can ignite in contact
with strong oxidants.
Ammonia requires a concentration of at
least 15% and the presence of a source of ignition to explode.
Ammonia can explode in contact with strong oxidants.
Ammonia is mainly absorbed by the
respiratory tract. Absorption by other routes is
negligeable.During a short-time exposure (up to 2 minutes) at
concentrations varying between 57 and 500 ppm, 83 à 92 % of
the inhaled dose is retained in the respiratory tract (mouth,
lungs, etc.), among volunteers. Following longer exposures (30
minutes) among seven (7) volunteers exposed at 500 ppm, it has
been reported that the retention of ammonia in the mucous
membranes of the nasopharynx diminishes to 23 % when equilibrium
is achieved (after10 à 27 minutes).
The few data available in man suggest
that only small amounts are absorbed into the blood circulation.
Blood ammonia is distributed throughout the body where it plays an
important role the synthesis of proteins and in maintaining the
Ammonia is an essential constituent of
the human body. It is produced during digestion and rapidly
metabolized into glutamine and urea, mainly by the liver.
The major part of ammonia (70-80%)
dissolved in the mucous membranes of the upper respiratory tract
was excreted unchanged in the expired air following inhalation at
500 ppm during 10 to 27 minutes by volunteers. Ammomia absorbed by
the body is excreted by the kidneys as urea and ammonia compounds.
Less than 1% of the 4 grams of ammonia produced daily by the
intestinal tract is excreted in the feces. A certain amount may
also be excreted in sweat.
II-Acute Effects :
Irritation and corrosion :Ammonia being
absorbed very little by the body, its effects are limited to its
irritating and corroding capacity to the eyes, the skin and the
Ammonia as a gas is irritating and
corrosive to the skin, the eyes and the higher respiratory tract
(nose and throat). The severity of symptoms may vary according to
the conditions of exposure (duration of contact, concentration of
the product, etc).
The first signs of exposure are
discomfort, dry nose, watering and a burning sensation in the
Exposure to high concentrations may
cause irritation of the skin, damage to the cornea, cough, pain in
the chest, respiratory problems (dyspnea i.e. shortness of breath)
In severe cases, one observes laryngeal
oedema which may evolve to pulmonary oedema and death by
asphyxiation. The symptoms of pulmonary oedema (mainly cough and
other respiratory difficulties) often appear after a delay which
may go up to 48 hours. Physical exertion may worsen these
Rest and medical surveillance are
Accidental exposure to high
concentrations can also cause a bronchial irritation
(RADS, Reactive Airways Dysfunction
Syndrome, an asthma-like condition or asthma without a latency
Very high concentrations may lead to
corrosion of the skin, eyes and upper respiratory tract.
Contact with liquified ammonia gas can
cause frostbites as well as corrosion of the eyes and the skin,
following a direct contact.
Probable effects following
Discomfort among non-accustomed
(Quebec's time weight average
32-50 (5 mn)
Nose dryness, slight irritation
of the nose and throat.
(Quebec's short term exposure
135 (5 mn)
Eye irritation, watering.
Irritation of nose and throat.
Rapid death by suffocation or by
accumulation of fluids in the lungs.
IV-Chronic effects :
Repeated or prolonged exposure can
generate a certain tolerance, i.e. the irritating odor and effects
will be felt at higher concentrations.
Available data do not show that ammonia
can cause cutaneous or respiratory sensitization
Justification of effects :
Some reports mention cutaneous eruption
(urticaria) following exposure to the vapors of ammonia and
asthma-like reactions following exposure to concentrations between
8 to 15 ppm of ammonia. However, these reports do not make it
possible to link these effects with a mechanism of allergic
VI-Effects on development :
No data concerning an effect on the
development was found in the consulted documentary sources
Justification of effects :
Ammonia is produced by the body. It is
also an essential constituent for the normal development of human
beings. An exposure in the work environment is not very likely to
lead to an increase in the blood ammonia level and thus, it does
not represent a hazard to development.
VII-Effects on reproduction
No data concerning the effects on
reproduction was found in the consulted documentary sources.
Justification of effects :
Ammonia is normally produced by the
body. It is also an essential constituent for the normal
development of human beings. An exposure in the work environment
is not very likely to lead to an increase in the blood ammonia
level and thus, it does not represent a hazard for reproduction.
VIII-Effects on breast milk :
It is detected in human mother's milk.
Justification of effects : Ammonia is a
natural component of this milk.
IX-Cancinogenic effects :
There was no data concerning a
cancerogenic effect found in the consulted documentary sources.
X-Mutagenic effects :
The data do not make it possible to make
an adequate evaluation of the mutagenic effect.
Justification of effects :
A study mentions a light increase in
chromosomal aberrations and sister chromatid exchanges in workers
of a manufacture of artificial fertilizers simultaneously exposed
to several chemicals among which ammonia.
First Aid :
In the event of inhalation of gas, bring
the worker in a ventilated place and place him in semi-seated
position. If he does not breathe, give him artificial respiration.
In the event of respiratory difficulties, give him oxygen.
Transfer immediately him to the nearest medical emergency
department. The symptoms of pulmonary oedema may appear after a
delay of several hours and are worsened by physical exertion. Rest
and medical supervision are consequently essential.
II-Contact with eyes :
Rinse the eyes copiously with water for
at least 20 minutes. See a doctor.
III-Contact with skin :
Quickly withdraw contaminated clothing
by using suitable gloves. Abundantly rinse skin with water. See a
In the event of a frostbite, apply
lukewarm water, rinse abundantly and see a doctor
II-Valeur d'exposition de courte
durée (VECD) , (TLV-STEL)
35 ppm 24 mg/m³
When engineering measures and
modifications of working methods are not sufficient enough to
reduce the exposure to this chemical, the wearing of individual
protection equipment may be necessary. These protection gears must
be in conformity with regulation.
I-Respiratory tract :
Wear a respiratory protection apparatus
if the concentration in the work environment is higher than VEMP
(25 ppm or 17 mg/m³) or than the VECD (35 ppm or 24
Wear skin protection. The selection of
skin protection equipement depends on the nature of the work to be
Wear protection for the eyes if there is
a risk of splashes. The selection of ocular protection depends on
the nature of the work to carry out and, if it is necessary, on
the type of apparatus of respiratory protection used.
2-Toxicologie Industrielle et
Intoxications Professionnelles, Lauwerys R. last
3-Sax's Dangerous Properties of
Industrial Materials, Lewis C., last edition.
4-Clinical Environmental Health and
Toxic Exposures, Sullivan J.B and Krieger G.R., last
By Edouard Bastarache
Article by Edouard Bastarache Edouard Bastarache is a well known doctor that has written many articles on the subject of toxicity of ceramic materials and books on technical aspects of ceramics. He writes in both English and French.