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: 
 
• Properties 
• 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. 
 
 
2. Properties 
 
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-
dyed shades. 
 
  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. 

4. Application
 
• Substrate 
 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 
Shades 
Sanodal® Gold 
4N 
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 
• Sealing 
 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 
dyeing process. 
 
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. 
 
5.7 Disposal 
  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® 
WT-1 Liquid". 
 
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. 
 
• pH 
  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 
  Reagents 
• 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 
solution. 
•   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%. 
 
  Analysis procedure 
  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). 
 
  Calculation 
  Concentration of Sanodal® Gold 4N in g/l:  
   C4N⋅=b    3.6 
  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%. 
     
   
COx=  33.3a 
b
         
   COx 
  pure Sanodal® Gold 4N = 100% 
  with excess oxalate > 100% 
  with insufficient oxalate < 100% 
  minimum value = 110% 
 maximum value = 140% 

6.2 Proof of ferrooxalate 
  Reagents 
• 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% 
 
  Identification reaction 
  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 
 
  Reagents 
• Potassium iodate starch paper 
 
  Identification reaction 
  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 
H2O2 reaction. 
 
 
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). 
 
7.1 Substrate 
  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. 

7.3 pH 
  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 
necessary. 
 
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. 
 
8.1 Alkalis 
  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 
the pH. 
 
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. 
  Survey 
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.
precipitate 
calcium 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 
• pH 
  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 
Section 5.8. 
 
 
  Note 
  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 
ferrioxalate. 
 
 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.