The Techniques of Holocaust Denial: Leuchter, Rudolf and the Iron Blues

Writer: Richard Green


ABSTRACT: Leuchter and Rudolf have published pseudoscientific reports purporting to show that chemical residues president in the gas chambers of Auschwitz-Birkenau are incompatible with homicidal gassings. Markiewicz, Gubala, and Labedz have shown unequivocally that cyanides are present in Kremas I-V and bunker 11, at levels above background levels measured in other facilities. Many of the delousing chambers exhibit blue-staining that is not obviously present in the homicidal gas chambers. Leuchter and Rudolf found higher levels of cyanide in these installations than they found in the homicidal gas chambers. The blue-staining present in the delousing chambers is most likely one of the iron blues, a class of compound including Prussian blue. Markiewicz, Gubala, and Labedz discriminated against the presence of this compound, whereas Leuchter and Rudolf did not. The findings of Leuchter and Rudolf do not contain much information beyond what is already obvious to the naked eye. Understanding the formation of Prussian blue is essential to understanding the importance of the findings of Markiewicz, Gubala, and Labedz. Industrial methods of producing Prussian blue are reviewed briefly. Rudolf’s proposed mechanism of Prussian blue formation is examined. It is unlikely that Prussian blue would have formed in the gas chambers under the conditions under which they were operated. Slight variation in conditions could change that probability and that is perhaps the explanation for the presence of Prussian blue in the delousing chambers and the gas chamber at Majdanek. Alich et al. Found that the formation of Prussian blue is extremely sensitive to cyanide concentration and pH. Several attempts to make Prussian blue form exposing construction materials to HCN failed. The burden of proof that Prussian blue must have formed under the conditions present in the gas chambers in on the deniers.

Recently a number of “forensic” reports presented by Holocaust-deniers purport to show that homicidal gassings at Auschwitz-Birkenau (AB) did not occur. The agent of murder in the gas chambers of AB was Zyklon-B. Zyklon-B is a solid support impregnated with hydrogen cyanide. A discussion of the chemistry of mass murder with Zyklon-B as well as an analysis of several of these pseudoscientific reports and a real forensic analysis don by the Institute for Forensic Research in Cracow (IFRC) can be found in the article The Chemistry of Auschwitz. Germar Rudolf 1 among others has made the claim that homicidal gassings could not have occurred in the homicidal gas chambers of AB. His argument relies on the fact that there is blue staining present on facilities where Zyklon-B was used for delousing but no apparent staining in the facilities in which Zyklon-B was used for homicidal purposes. He claims to have measured more cyanide content in the stained walls than in the unstained walls and concludes that the levels of cyanide present in the homicidal gas chambers are not consistent with homicidal gassing. Leuchter 2 has also made analogous measurements with analogous claims.


Presence of Cyanides in Gassing Facilities and Apparent Absence of Prussian Blue

Markiewicz, Gubala, and Labedz of the Institute for Forensic Research, Cracow demonstrated that HCN was present in the homicidal gas chambers, i.e., Krema I, Krema II, Krema III, Krema IV, Krema V, and the cellars of Bunker 11, at levels above other facilities in the AB complex. 3 They took several samples from Bunker 11, and Kremas I-V. They found levels of cyanide significantly higher than background levels in all of these sites of homicidal gassing. They used a carefully calibrated method in which their calibration curve was checked with known standards in the process of running the sample. The analysis was conducted by a separate team from the sample collection team to insure objectivity. Unlike the Holocaust-deniers, they used a carefully calibrated method that discriminated against the iron blue compounds, such as Prussian blue , that are believed to be responsible for the above-mentioned staining.

The purpose of this essay is to look closer at this blue staining, what it is, how it could have formed, and whether its absence in the homicidal gas chambers of AB can reasonably be interpreted to mean that homicidal gassings did not take place there. Owing to the fact that Rudolf and Leuchter did not discriminate against iron blue compounds, the fact that they measure more cyanide compounds in the delousing chambers than in the homicidal gas chambers is functionally no different than the observation that the blue-staining is present in the delousing chambers and not in the homicidal chambers. In other words, they have found nothing by measurement that is not apparent without measurement. By a carefully thought out experiment, Markiewicz, Gubala, and Labedz have provided real information.

The fact that there is obvious blue-staining in the delousing chambers and not in the homicidal chambers of AB is not in dispute here. It should be mentioned, however, that at the Majdanek death camp there is indeed blue-staining on the homicidal gas chambers. 4,5 Additionally, the staining is not present on all known delousing chambers. One is left immediately to ponder why it would be argued that such staining is a necessary consequence of the use of hydrogen cyanide (HCN).

Owing to the fact that he cannot think of a mechanism by which the Prussian blue could form from iron in its third oxidation state (as present in brick), Bailer 6 speculates that the presence of iron blues may be because of paint rather than exposure to HCN vapor (iron blues are commonly used as pigments in paints). Bailer’s speculation, although it is certainly more reasonable than the claims of Rudolf that homicidal gassings did not occur at AB, must still be viewed with skepticism. If paint was indeed used on these facilities, it should be possible to find evidence that such paint was purchased and applied. The paint hypothesis needs more evidence to support it, if it is to be believed.

A few points should be made clear:


  1. Some of the delousing chambers exhibit blue-staining, whereas some of the homicidal gas chambers do not. Because Rudolf and Leuchter chose to include this blue-stained material in their samples, their measurements do not provide more information than visual inspection except as an exercise in fooling the public by putting numbers to what is apparent to the eye. In other words, by not discriminating against Prussian blue they have introduced a bias into using the delousing chambers as a control. They have not thereby contributed to understanding why a discrepancy in the level of Prussian blue exists. 
  2. The blue-stained material is characteristic of a class of compounds called the iron blues, of which Prussian blue is a member. Although Bailer4 has suggested that the blue color may come from paint, that explanation seems unlikely. Observers of the staining at Majdanek describe it as splotchy and saturated deep within the building materials. 
  3. In order for Prussian blue to form, it is necessary either to have a source of Fe(II), Fe(0), or an agent that can reduce Fe(III) to Fe(II). If a reducing agent is present, the conditions must be right to cause reduction. This point is explained further in some depth, below. 
  4. The Institute for Forensic Research, Cracow, discriminated against Prussian blue compounds so as not to introduce a bias in the control. They found unequivocally, that all buildings said to have been in contact with HCN at Auschwitz-Birkenau had traces of cyanides significantly above the background of other buildings at Auschwitz-Birkenau.

Prussian blue once formed is much less susceptible to weathering than are other forms of cyanides. Rudolf himself acknowleges this fact: 4


If the hydrocyanic acid from the Zyklon B had bonded with the brickwork only through the process of adsorption, then due to the volatility of hydrocyanic acid (boiling point: 25.7C) it would no longer be possible today to detect any hydrocyanic acid residues in the remaining walls.

This argument neglects the fact that hydrogen cyanide is a weak acid that can form salts, such as potassium cyanide, fails to address the binding of chemisorption, or the formation of other cyanide compounds; yet the point is not completely without merit. More significant, perhaps, is the fact that cyanide salts are highly water soluble unlike Prussian blue. Markiewicz et al. report that they were not optimistic at being able to detect cyanides so many years after exposure to HCN. Owing to the fact that they had legal access to their samples, however, they were able to plan sample collection in a manner likely to detect cyanides in locations that were relatively sheltered from the elements. The fact that they measured traces of cyanide not bound to iron in the homicidal gas chambers at levels above those observe in other buildings disproves the claims that such traces would not be measurable

In order for Leuchter or Rudolf to demonstrate the significance of their findings, it is necessary for them to prove the necessity of Prussian blue formation under the conditions that the homicidal gas chambers were operated. Showing that the delousing chambers have Prussian blue and that the homicidal gas chambers do not, proves nothing, if it cannot be shown that conditions in the gas chambers were such as to produce Prussian blue. I shall therefore turn my attention to Prussian blue, its formation and the conditions present in the gas chambers.


The Iron Blues and Their Industrial Preparation

There are a number of compounds known colloquially as the “iron blues.” Insoluble Prussian Blue, for example, is Fe4[Fe(CN)6]3. It can be formed by the addition of Fe(II) to [Fe(III)(CN)6]-37 It should be noted here that the distinction between soluble and insoluble is a matter of the ease with which the compound forms colloidal suspensions rather than any real difference in solubility. 7 This point is important when addressing the possible degradation of Prussian blue. While I will not argue that degradation of Prussian blue is the cause of its absence from the homicidal gas chambers, this hypothesis should not be rejected as a possibility out of hand.

There are 3 methods generally used for the preparation of soluble iron blues described by Holtzman. 8 Insoluble blues can be prepared by subsequent reaction of soluble blues with various metal cations (See table II in Holtzman). The three methods are

  1. mixing a ferric (Fe(III)) salt with a ferrocyanide Fe(II),
  2. mixing a ferrous (Fe(II)) salt with ferricyanide Fe(III), and
  3. mixing a ferrous salt with a ferrocyanide, followed by oxidation.

It should be noted that it is necessary to produce iron in a mixture of oxidation states or perhaps in a resonance structure of mixed states. Bailer argues for the improbability of Prussian blue formation for exactly that reason.


Rudolf’s Proposed Mechanism

Rudolf, 1,4 in his own persona and also under the alias 9 “E. Gauss,” 10 has with some bombast criticized Bailer for not noting the possibility that HCN itself could be the reducing agent responsible for converting iron (III) into iron (II). Even stranger synthesis of iron blues have been reported. 11 Rudolf cites in support of his claim a paper by Alich, Howarth, and Johnson.12 Apparently, did not read this paper very carefully. The authors investigate the reduction of [Fe(CN)6]3- by aqueous and ethanolic solutions of CN. They suggest that CN is indeed the reducing agent, but their inability to observe CNO must suggest that this claim is inconclusive. DeWet and Rolle have claimed that Fe(III)Fe(III)(CN)6 can be reduced to a Prussian blue compound with water. 13 The observation by Alich et al. that addition of water inhibits the reaction, perhaps, makes the supposition that HCN is the reducing agent more plausible despite their inability to observe CNO

What the reducing agent is, however, may be academic. The relevant question is whether such a mechanism to form Prussian blue would necessarily have been operative in the gas chambers.

Alich et al. show that Prussian Blue does not form in water unless there is an excess of CN ions compared to Fe(III) or very basic conditions. <ahref=”blue-notes.html#note-14″>14</ahref=”blue-notes.html#note-14″>


The dilution of the absolute stock solutions of Fe(III) and Fe(CN)63-with absolute ethanol gave the red complex which persisted for about 1 hour, as compared to the disappearance of the red complex in the aqueous media at a dilution of 3.3 * 10-4 M. The red complex in ethanol darkened within the hour and reduction to Prussian Blue was complete in 2 days (Fig. 3).

Now comes the important part:


It is to be noted that the complex in aqueous solution, under the same conditions, decomposes immediately, the spectrum reverting to that of the Fe(CN)63- ion. Furthermore, addition of as little as 13% water (by volume) caused the red complex to decompose, giving a spectrum of the Fe(CN)63- ion.


Conditions in the Homicidal Gas chambers at Auschwitz Birkenau.

In other words, Prussian blue only forms with very high concentrations of CN. The concentrations in the gas chambers were such that ambient water at equilibrium might at most have reached concentrations on the order of 0.1 M as shown in Appendix I That such an equilibrium concentration could have been reached during the time span of an actual gassing is doubtful. This concentration is the equilibrium value. Absorption of HCN by water would undoubtedly be kinetically limited, i.e., the concentration would be limited by how fast the absorption process can occur. The equilibrium concentration assumes that the water has been exposed to HCN long enough that the rate of HCN leaving solution into the gas phase is equal to the rate at which HCN from the gas phase is being absorbed by the water.

Most importantly one must recall that the gas chambers were hosed down with water after gassings to clean up blood and excrement.15 Considering that the ambient water would have been quite small, providing 100 times dilution would have been trivial. This effect may actually be the explanation for the presence/absence of Prussian blue in the delousing/homicidal gas chambers, but some further research will be necessary to support this supposition conclusively.

Prussian blue formation is exceedingly sensitive to concentration and also to pH. Very small effects could tip the balance between whether Prussian blue forms or not. Alich et al. found a strong pH dependence to the reaction. The presence of human beings in the gas chambers could also help tip the balance. CO2 is an acid anhydride and there would have been a lot of it in the homicidal chambers. An acid anhydride is a substance that increases the acidity of a solution when it becomes solvated. Even atmospheric concentrations of CO2 (at 360 ppm today, about 330 ppm then) are sufficient to cause pure rain water to have a pH of 5.6. Human beings exhale about 4% CO2, so the pH could be quite a bit lower. For example at 2 % CO2 the pH would be below 4.8. Appendix II derives the relationship between carbon dioxide concentration and pH.

Low pH inhibits the reaction. Additionally, a lower pH will drive the HCN from solution, making the CN more dilute at the outset. These considerations may be somewhat mitigated by the use of limewash (Ca(OH)2) which is slightly water soluble and could boost the pH. A pure solution of Ca(OH)2 can reach a pH as high as 12 (Cf. Merck Index), but coatings with limewash hardly provide such conditions.

Another point should be noted here. The conditions outlined here are for the formation of Prussian blue in the presence of cyanide ions and Fe(CN)63-. In the gas chambers Fe(III) would have been present in the brickwork and cyanide ions from the HCN itself, but Alich et. al. note: “The spectra of solutions containing only Fe(III) and CN ion indicated only the acid hydrolysis of Fe(III).” .16 Prussian blue did not form.

The experimental evidence that Prussian blue formation is not a necessity with the presence of HCN and construction materials is strong. Markiewicz et al. 17 were not able to produce such pigments in experiments with HCN and building materials. Additionally, Rudolf did an experiment in which he exposed a brick to HCN and yet found no detectable level of cyanides whatsoever.. 18 These failures to produce Prussian blue are sufficient to demonstrate that its formation at detectable levels is not a necessary result of exposure to HCN.



Whereas it would be premature to claim that I have explained why Prussian blue is present in the delousing chambers and not in the gas chambers, I have certainly shown that Rudolf’s proposed mechanism is unlikely to have been operative in the homicidal gas chambers. More importantly, I have shown that the formation of Prussian blue is subject to very subtle influences of the conditions present. Slight changes in condition may have been sufficient to push the balance one way or the other. Yet the burden of proof here lies with the deniers. They claim to prove that gassings could not have occurred in the gas chambers. To make such an argument, they need to demonstrate that their proposed mechanism of Prussian blue formation must be operative in the gas chambers under the precise conditions under which they were operated. Their task in daunting. Any claim made on the basis of the absence of Prussian blue is at best empty speculation. Add to that the evidence that cyanides were indeed present in the homicidal gas chambers, that witnesses claim that gassings took place there, that the perpetrators admitted to their crimes, and that 1 to 1.5 million people were deported to Auschwitz-Birkenau and never returned and we can label Rudolf’s work willful distortion of the evidence.