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SANODAL GLOD 4N
Sanodal® Gold 4N
For gold shades of high fastness on anodised aluminium
Sanodal® Gold 4N is a water-soluble product based on ferrioxalate for the chemical dyeing of
artifically produced oxide films on aluminium in gold shades of high fastness.
This technical information bulletin contains the following information on the features and application of
Sanodal® Gold 4N:
• Optimum application and working method
• Maintenance of dyebaths
• Analytical methods of bath monitoring
• Influence of processing parameters and dyeing conditions
• Factors impairing bath stability.
1. Brief characterization
Sanodal® Gold 4N is a ferrioxalate-based preparation in powder form. This Sanodal® product
is for attaining gold shades of high fastness on artificially produced aluminium oxide films.
Compared to conventional ammonium ferrioxalate, Sanodal® Gold 4N is distinguished by
higher photochemical stability in solutions.
Commercial form greenish yellow powder
Storage stability practically unlimited. Protect product from effects of light and
moisture. Any lumps that may form have no influence on the
product's dyeing properties.
Solubility at 25°C: 430 g/l water
at 65°C: 750 g/l water
Bulk density 550 g/l
pH of product 4.0 ± 0.5 at 30 g/l
Ecotoxicological data see Safety Data Sheet.
3. Scope of application and colour scale
Aqueous Sanodal® Gold 4N solutions can be used to produce gold shades of high fastness to
light, weather, corrosion and heat on chemically or - preferably - anodically produced oxide films
on aluminium and its alloys. The dyeings are produced by the hydrolytic incorporation of
inorganic hydrated iron oxide colour pigments in the oxide film.
The colour scale depends on the working method and ranges from new silver to pale brass to
gold tones of extremely varied degrees, even to brownish orange. The colour scale can be
extended even to attractive browns by overdyeing aluminium sections that have been
electrolytically precoloured in bronze tones.
Sanodal® Gold 4N solutions can also be used to decolourize difficult-to-remove adsorption-
Thanks to their high resistance, Sanodal® Gold 4N-dyed aluminium sections can be used in a
wide variety of industrial applications, e.g. the finishing of audiovisual equipment, jewellery,
signs and nameplates, household articles and, in the framework of the Sanodal System, also
for facade elements in the construction industry.
Chemically or - preferably - anodically produced unsealed oxide films on aluminium or its
alloys (whether uncoloured or electrolytically precoloured).
• Application technique
Immersion in aqueous solutions with bath agitation, or by spraying.
• Water quality
It is recommended to use deionized water.
• Application amounts
pale 10 - 20 g/l
medium to deep 20 - 30 g/l
• Dyeing temperature
40-55°C, for pale shades also 30-40°C
• pH of baths
between 4.0 and 5.0
• Dyeing time
0.5 - 20 min, depending on desired shade, but preferably for 2-10 min
The dyed oxide films must afterwards be sealed according to the guidelines for anodized
aluminium. It is recommended to seal in boiled water with 2 ml/l Anodal® SH-1 Liquid.
5. Dye solutions - setting, application, maintenance
5.1 Dyebath and feed tanks
The ideal material for the dyeing tanks and feed equipment is acid-resistant high-grade steel
based on Cr, Ni or Mo. Tanks made of normal steel and aluminium with acid-resistant, inorganic
or organic-based linings (enamel, rubber, polyester, polyvinyl chloride, etc.) are also suitable.
However, it should be borne in mind that even tiny leakages can result in an impairment of the
5.2 Setting and reinforcing dyebaths
Before being added to the bath, Sanodal® Gold 4N must be dissolved in at least three times
the amount of water, which should be as hot as possible.
5.3 Water quality
Deionized or very soft water should be used. If no such water is available, it is essential to add
2-5 g/l oxalic acid.
5.4 Bath circulation
For high uniformity of dyeings, the dyebath must be kept in moderate agitation shortly before
and during the dyeing process, e.g. by blowing in air through pipes or with a circulation pump.
5.5 Standing time and service life of dyebaths, consumption of product
With careful adherence to our recommendations, dye solutions can be used almost indefinitely.
In our experience, the service life of dyebaths, with normal throughput and minimal
maintenance expenditure, lasts from 6 months to 2 years.
Depending on the depth of shade, the consumption of the product for pigmentation is between
0.1 and 10 g/m2 Sanodal® Gold 4N.
The drag-out loss ranges from 1.5-5 g/m2. Depending on the shade depth, the guide value for
overall consumption, including bath renewal is 20-30 g/m2 Sanodal® Gold 4N.
5.6 Storage of dye solutions
When not in use, the Sanodal® Gold 4N solution should be immediately protected as far as
possible from light and air by covering the dyeing tank or storage in a closed tank.
Disposal of spent dyebaths must be carried out in accordance with local wastewater regulations
according to the recommendations given in our technical information bulletin entitled "Anodal®
5.8 Control and reinforcing of the dyebath
For dyebath maintenance, in addition to constant monitoring of the dyeing properties, the
control operations and correctional measures described below must be used. It is
recommended to carry these out periodically using experiential values, especially when
problems occur and after prolonged non-use of the bath.
• Sanodal® Gold 4N concentration
This measurement is carried out as described in Section 6.1. If the concentration is found to
be inadequate, add the calculated amount of Sanodal® Gold 4N in concentrated form.
• Relative oxalate concentration
This is also determined as described in Section 6.1. The actual oxalate content must
correspond at least to the concentration calculated on the composition of Sanodal® Gold 4N
(= 100%). This has been found to range from 110 to 140%. If the measured value is less
than 110%, add 2-5 g/l oxalic acid.
The pH of the dyeing solution can be measured with the aid of a pH meter. For a quick
measurement, pH indicator paper can also be used.
In case of deviation from the recommended pH range between 4.0 and 5.0, the pH is
corrected with dilute sulphuric acid, or else with dilute caustic soda solution or ammonia.
• Appearance of separated decomposition products
Sanodal® Gold 4N forms clear, greenish yellow solutions; these charracterize an excellent
condition of the bath. When the greenish tinge disappears, the colour shifts to brown or
cloudiness occurs and decomposition as described in Section 8 is present.
6. Analytical monitoring of Sanodal Gold 4N baths
6.1 Titrimetric analysis
• 0.2 N-KMnO4 (potassium permanganate)
In a measuring flask, dilute a normal concentrate (e.g. Titrisol+ Merck No. 9935) adjusted
for the preparation of 1 litre of a 0.1 N solution, to 500 ml.
Concentration: 6.32 g potassisum permanganate in 1000 ml solution.
• M-EDTA (ethylene diamine tetraacetic acid)
In a measuring flask, dilute a normal concentrate (Titriplex+ III Merck No. 9992) adjusted
for the preparation of 1 litre of a 0.1 N solution, to 1000 ml.
Concentration: 37.2 g ethylene diamine tetraacetic acid, disodium salt, MW 372, in 1000 ml
• Buffer/Indicator solution
164 g sodium acetate anhydrous p.a. (MW 82)
100 g chloracetic acid cryst. pure (MW 94.5) and
10 g 5-sulphosalicylic acid pure (MW 254.2) as indicator
have to bedissolved in deionized water, and diluted to 1000 ml in a measuring flask .
• Sulphuric acid 20%.
Take a sample from the production dyebath and clarify by filtration, e.g. through a folded paper
filter, discarding any cloudy first runnings. Using a transfer pipette, take 20 ml of the clear filtrate
and, while heating and stirring, add this to 100 ml deionized water and 10 ml sulphuric acid
20%. When this solution reaches 50-60°C add dropwise from a burette 0.2 N-KMnO4 until the
yellowish solution takes on a steady pale pink coloration.
Consumption: a ml 0.2 N-KMnO4 (ca. 25 ml with 30 g/l Sanodal® Gold 4N)
At the same temperatuare, now add 20 ml buffer/indicator solution. Add dropwise from another
burette 0.1 M-EDTA to this cloudy red mixture until the red colour disappears.
Consumption: b ml 0.1 M-EDTA (ca. 8 ml with 30 g/l Sanodal® Gold 4N).
Concentration of Sanodal® Gold 4N in g/l:
Relative concentration of the oxalate in % :
The relative concentrations indicates the molar oxalate/iron ratio, where the ratio 3 moles of
oxalate (264 g) to 1 mole of iron (55.9 g) is defined as 100%.
pure Sanodal® Gold 4N = 100%
with excess oxalate > 100%
with insufficient oxalate < 100%
minimum value = 110%
maximum value = 140%
6.2 Proof of ferrooxalate
• Potassium ferricyanide 5%
Disssolve 5 g potassium ferricyanide (red prussiate of potash) in 100 ml deionized water.
Store this reagent in the dark.
• Sulphuric acid 20%
To approx. 2 ml of the unfiltered dyeing solution, add 2 drops of sulphuric acid 20% and 2 drops
potassium ferricyanide 5% and boil up for a short time. A blue-green colour indicates the
presence of ferrooxalate, which is produced by the decomposition of Sanodal® Gold 4N under
the effect of light or metal. The blue coloration must appear immediately.
6.3 Proof of hydrogen peroxide
• Potassium iodate starch paper
On the reagent paper, place a drop of the acid dyeing solution to which H2O2 has been added
for the purpose of regeneration. A violet coloration indicates the presence of H2O2.
Note: Make further additions of H2O2 only in the case of a positive ferrooxalate and a negative
7. Notes on dyeing
The final shade depth depends on the properties of the anodic film (thickness and porosity) and
the dyeing conditions. The parameteres are defined on the basis of laboratory trials or
experiential values so that the film can achieve the required protective effect and the desired
shade can be produced within the defined processing time. For high reproducibility, the
parameters, once defined, must be adhered to as exactly as possible by monitoring the
oxidation and dyeing process. Any deviations must be offset by adjusting the dyeing time
(sampling by comparison with a standard dyeing sample).
The shade depth increases along with increasing thickness and porosity of the anodic film.
These two influential factors depend in turn on the alloy, anodizing time, temperature, current
density and composition of the acid electrolyte.
7.2 Sanodal Gold 4N concentration
The exact concentration of Sanodal® Gold 4N in the bath is not to be regarded as a critical
factor, and normal fluctuations have practically no effect with short dyeing times (pale gold
shades). It is recommended, however, especially in cases where the dyeing power deviates
distinctly from the normal, to monitor the concentration of the dye in the bath.
Owing to the drag-in of anodizing acid as well as film detachment and the effect of air and light,
the pH value can change, despite its inherent buffering. As a rule, under production conditions a
gradual rise in the pH is observed.
At pH values below 4 the dyeing power diminishes rapidly, and at pH values over 6, hydrolysis
takes place with the precipitation of ferrihydroxide.
7.4 Dyeing temperature
With rising temperature of the dyebath the rate of dyeing greatly increases. In order to achieve
acceptable dyeing times, it is preferable to use the lower temperature range (30-40°C) for pale
shades and the upper range (40-55°C) for deeper tones. Above 60°C the maximum attainable
shade depth becomes progressively lower as a sealing effect sets in.
Low dyeing temperatures can later facilitate any stripping of the dyeing which may become
7.5 Dyeing time
By adjusting the dyeing time, a wide range of colours can be covered. The other operating
parameters such as film structure, dyeing temperature and dyestuff concentration should be
selected so that the desired shade is produced in a time span ranging from 30 s to 30 min,
preferably within 2-5 min.
For reasons of shade uniformity, especially with large-surfaced aluminium parts, dyeing times of
less than 30 s should be avoided.
Once the dyeing time is set, it should not be deviated from by more than 10 s for pale dyeings
and 1 min with deep shades.
7.6 Additions for stabilization of the solution
Sanodal® Gold 4N exhibits extremely high solution stability in the presence of oxygen and
excess oxalate. For this reason it is recommended to add 2-5 g/l oxalic acid and to circulate air
through the bath while it is in use.
The oxalate is used up due to the action of air and light. On the other hand, the dyeing power
decreases with increasing oxalate concentration. For this reason it is essential to keep the
oxalate concentration within the defined limits by periodically checking the relative oxalate
concentration according to Section 6.1 and to supplement it as necessary.
8. Notes on bath maintenance
Apart from the consumption related to processing, Sanodal® Gold 4N solutions exhibit only
limited stability. This applies even more strongly to the usual commercial ammonium
ferrioxalates. Observance of the following recommendations as well as those in Section 5 will
ensure virtually unlimited service life of the dyeing solutions.
If the pH exceeds the upper limit value, hydrolysis takes place and a gel-like, brown ferrioxide
hydrate precipitates. This can be corrected, as described in Section 5.8.
8.2 Effect of air
The effect of atmospheric oxygen results in oxidative degradation of the oxalate. On the other
hand, oxygen counteracts the decomposition due to light described below in Section 8.3 by
keeping the iron at the higher, "ferri" stage, which is effective for dyeing. For this reason it is
recommended to introduce air into the bath during its exposure to light, i.e. while it is in use, or
even to add hydrogen peroxide. However, this entails the periodical replacement of the
degraded oxalate, as described in Section 5.8. Otherwise brown ferrioxide hydrate will
precipitate, despite maintenance of a constant pH. Degradation of the oxalate involves a rise in
8.3 Effect of light
Due to the effect of light, the dissolved Sanodal® Gold 4N undergoes a photochemical,
intramolecular reaction and decomposes into ferrooxalate, which is ineffective for dyeing
purposes. This slowly precipitates as a fine crystalline, yellowish suspension. Oxygen and
oxalate counteract this reaction. Any ferrooxalate which has formed can be converted back into
Sanodal® Gold 4N by adding hydrogen peroxide and oxalate (see Section 5.8).
8.4 Water hardness
Water hardness extracts the oxalate from Sanodal® Gold 4N and precipitates it in the form of a
white suspension of earth alkali oxalates. The results correspond to the oxidative degradation of
the oxalate described in Section 8.2.
8.5 Contact with base metals
On contact with base metals such as normal steel or non-anodized aluminium, ferrooxalate is
formed. Its appearance and correction are described in Section 8.3 above.
8.6 Bath contamination
The state of the solution and the dyeing power are not greatly affected by the drag-in of
anodizing acid (sulphates, aluminium). For this reason, no special requirements are demanded
for the rinsing operation. However, the entrainment of other chemicals must be avoided,
especially phosphates and hardness elements from degreasing, lustre or etching baths.
9 Summary of measures to be taken
All the reactions mentioned in Sections 8.1 to 8.5 cause a reduction in the concentration of
Sanodal® Gold 4N. This reduction is not critical and can be corrected by replenishing it, in the
same manner as the consumption of the dye for processing. Precipitations visible to the eye do
not affect the dyeing process and are not a disturbing factor. More serious, however, is the fact
that sparingly soluble decomposition products in a colloidal transition stage can impair the
uptake of Sanodal® Gold 4N - even when its solution is intact - by closing the pores of the film.
As a result, due attention must be given to proper maintenance of the dyebath. If the dyebath
continues to be used despite cloudiness, the restoration of the bath is made more difficult owing
to the ageing of the precipitates.
Alteraton Causes Corrective measures
Brown coloration, pH too high Correct the pH
precipitation of gel -like
ferrioxide hydrate Lack of oxalate due to Add oxalate, use deionized water, protect
- effect of air from effect of air when not in use.
- water hardness
Formation of Effect of light, contact Protect dyeing solution from effect of light
ferrooxalate, yellowish with base metals and air. Add hydrogen peroxide, add oxalate.
Separation of white Water hardness Use deionized water, add oxalate
The following recommendations can therefore be made for correct bath management:
• Sanodal® Gold 4N concentration
Determine as described in Section 6.1 and
Replenish as described in Sections 5.2 and 5.8
• Relative oxalate concentration
Determine as described in Section 6.1 and
Replenish as described in Sections 5.2 and 5.8
Determine and correct as described in Section 5.8
• Discoloration and clouding of dye solution
Correct as described in Sections 2 and 3.
If these measures are not adequate or if ferrooxalate is present in the bath (positive ferrooxalate
identification as described in Section 6.2), add oxalate and hydrogen peroxide as described in
These recommendations, especially the analysis specificatons, are based exclusively on the
specific properties of Sanodal® Gold 4N and do not apply to normal commercial ammonium
Many of their dyestuffs, pigments and chemicals are patented by Clariant Ltd. or ist affiliates in numerous industrial countries.
® Trademark registered by Clariant Ltd or Clariant GmbH in numerous countries.
* Trademark licensed to Clariant Ltd in numerous countries.
+ Manufacter’s registered trade mark.
The signs ®, * and + appear only at the first mention of the product.
The information and recommendations presented here were compiled with the utmost care, but cannot be extended to cover
every possible case. They are intended to serve as non-binding guidelines and must be adapted to the prevailing conditions.