Sanodure® Black CRO  
 
 

Homogeneous black dye with rapid adsorption for the dyeing of anodized aluminium. 
 
Sanodure® Black CRO is of primary interest for finishing processes in which rapid dye adsorption is 
desired and the fastness properties are of secondary importance. 
 
Only recommended for interior use. 
 
 1. Dye-specific properties  
 
Commercial form : black fine powder 
Chemical character : homogeneous azo dye, metal-free  
Storage stability : virtually unlimited (close package tightly after removal of dye) 
Bulk density : 830 g/l 
Solubility in water at 20°C : 40 g/l 
Shade : black (not suitable for grey shades) 
Intrinsic pH : 6-9 (at 10 g/l) 
Ecotoxicological data : see Safety Data Sheet. 
 
 
2. Application conditions
 
Concentration, dyeing temperature and time 
 
 Concentration Dyeng temperature Dyeing time 
Standard coatings (>10 µm) 10 - 20 g/l 25 - 60°C 10 - 30 min 
Continuous coatings (3-5 µm) 20 - 30 g/l 50 - 80°C 2 - 5 min 
 
Dyeing pH : 7.0 ± 0.5 
Adjustment and correction of the pH : with acetic acid or dilute caustic soda 
Water quality : preferably deionized 
Stability of the dyebaths : avoid pH values below 6 (gel-like precipitates are 
formed, tinctorial strength falls off) 
Sealing : preferably with Anodal® ASL (one or two stage). 
 
 
3. Preparation of the dyebath
 
When preparing the dyebath care must be taken that the dye is dissolved well. 
The dye is preferably dissolved in a separate container with hot water (80-90°C) (1 part to ca. 5 
parts water). This stock solution is then stirred into the dyebath. 
 

4. Scope of application 
 
Sanodure®  Black CRO is particularly recommended when the finishing process calls for rapid 
adsorption of the dye and the fastness properties are of less importance. 
 
This dye is of special interest for the following applications: 
- short time dyeing 
- cold dyeing 
- dyeing of continuously produced oxide coatings (coil anodizing or similar thin coatings) 
- dyeing of cast parts of high silicon content 
- dyeing of oxide coatings with low adsorption power. 
 
For building elements which require light and weather resistant finishing anodized to a coating 
thickness of 20 µm or more, the following special dyes are recommended: 
 
For exterior architectural aluminium (by the Sanodal process) : 
Sanodal Deep Black MLW 
Sanodal Black GL Paste 
Sanodal Deep Black H3LW 
Sanodal Deep Black HBL Liquid 
 
 
5. Remarks on application 
 
5.1  Behaviour in cold dyeing  
With 20 g/l Sanodure® Black CRO deep black dyeings can be produced under standard 
conditions at room temperature. 
 
5.2 Effect of entrained foreign substances in the dyebath  
 
Foreign substances Sensitivity 
Aluminium ions and sulphates little sensitivity 
Chromic acid tinctorial strength declines 
 
5.3  Strengthening the dyebath 
A reduction in tinctorial strength caused by impurities can be made good by adding fresh dye, 
provided it is within the normal limits. 
 
5.4  Behaviour of dyeings in the sealing solution 
 
Sealing solution Bleeding 
deionized water medium 
tapwater heavy 
with Anodal®  ASL low 
 
Note: cold dyeings tend to bleed more heavily than others. 
 

5.5  Prevention of mould formation : 
 An addition of an antimicrobial product can inhibit mould formation for a long time. We 
 recommend the addition of Nipacide CI 15 (See Technical Information) 25 – 50 mg/l. 
 
 
6. Fastness and other properties of the dyeings 
 
6.1  Light fastness (ISO 2135) 
 
Coating/dyeing Rating 
GS Standard 12 µm (20 g/l, 60°C, 15 min) 3-4 
GS Standard 20 µm (20 g/l, 60°C, 20 min) 7-8 
Continuous coatings 3-5 µm 2-3 
 
6.2  Heat stability 
- Assessment: poor (rating 2, red-brown) 
- Test conditions: coating thickness 12 µm 
 dyeing conditions 10 g/l, 20 min, 60°C 
 sealing with Anodal®  ASL 
 time 2 h at 200°C 
 
6.3  Strippability of unsealed dyeings 
 Unsealed dyeings are virtually unstrippable in diluted nitric or sulphuric acid.  
 They can be  stripped in nitric acid 10 % + potassium permanganate 5 %.  
 After the treatment in Potassium permanganate, neutralization must be carried out for 1-5 min 
 in a sodium bisulphite 5 % solution. 
 
Dyeings which have aged for a few days are not strippable. Freshly produced. 

7. Disposal of spent dyebaths  
 
Spent dyebaths must be disposed of with Anodal® WT-1 Liquid. The precipitation method is 
described in the Technical Information bulletin for Anodal® WT-1 Liquid.  
 
The table below gives the dosages necessary for precipitating Sanodure® Black CRO: 
 
Precipitation FeCl3, 40% Etching lye Anodal®  WT-1 Residual dye 
method 
ml/g dye ml/g dye ml/g dye Liquid in the filtrate mg/l 
A 1.0 - 0.7 < 1 
B 1.0 - 0.7 < 1 
C - 1.0 0.7 < 1 

 Many of their dyestuffs, pigments and chemicals are patented by Clariant in numerous industrial countries. 
® Trademark of Clariant registered in numerous countries. 
®* Trademark registered in numerous countries and licensed to Clariant. 
®+ Other Manufacturer'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.