Lead soaps in paintings: Friends or foes?

The origin(s) and role(s) of metal soaps in paints are a worldwide concern today. These hybrid compounds, containing both fatty acid chains and metals associated with a carboxylate function, are increasingly identified in paints. As reviewed in the first part of this work, the presence of metal soaps in paints is differently interpreted in scientific publications: metal soaps are sometimes considered to play a positive role as anchor points, during paint drying processes; they can also be considered as responsible for many degradation processes (protrusions, efflorescences, darkening, etc.). Their origins are also interpreted in various ways. In some paintings (in particular from the twentieth century), they have sometimes introduced on purpose, as additives, to modify the physical properties of the painting materials. In older paintings, metal soaps are usually thought to result from an uncontrolled reaction of oil with lead-based pigments, in particular lead white, red lead, and lead tin yellow. In the second part of this work, the review of historical recipes of lead-based paint shows an important number of recipes based on controlled mixing of oil with lead driers. In the third part, the experimental reproduction of such traditional recipes using walnut oil and litharge (PbO) shows that lead soaps can be formed, both in about one hour at ～100°C, or in about one month at room temperature. It shows as well that after a few years, litharge is no longer detected in the paint medium, while different lead carbonates are. Finally, the micro-infrared spectroscopy and micro-X-ray diffraction re-analysis of protrusions from a nine-year model painting shows together with lead soaps, the presence of Pb₅(CO₃)₃(OH)₂O (‘synthetic plumbonacrite’), an unusual phase recently observed in a protrusion from a painting by Vincent Van Gogh. This work highlights (i) the multiple origins and roles of metal soaps in paints and (ii) the importance of combining the analysis of fragments from historical paintings with the analysis and reproduction of historical recipes. In particular, we show that the components detected today in historical paintings may severely differ from those originally used or prepared by the painter, complicating the assessment of the painter's intentions. More than the presence of metal soaps, the key questions to be tackled should be about their origins and (re)mobilization.     

The Shaping of the Curriculum

Abstract

Curriculum design might appear to be a project for a pure educational theory. An example of such a theory is Paul Hirst's deduction of distinct forms of knowledge’ upon which rests his advocacy of the liberal curriculum’. Hirst's theory, though immune to many of the attacks that have been directed at it, fails to consider how (if at all) the structure of knowledge maps on to the structure of our mental (learning) faculties. The partitioning of the manifold of knowledge may correspond not at all to the optimum curricular partitioning of the teaching manifold. Further, as a curriculum proposal, Hirst's account needs to be underwritten by an account of the purpose of education. Accounts of the latter sort normally invoke considerations of a political nature. Such considerations, together with the influence of other forces, tend to pull curricula in directions which many educationalists regard as undesirable. Can pure educational theory reassert itself as the controlling force behind curriculum planning? I argue that there is little prospect of its so doing.     

From Brown to Ayers v. Fordice: the changing shape of racial desegregation in US higher education

Racial desegregation in higher education is taking on a new direction as the twenty‐first century approaches. The Brown v. Board of Education decision brought down legal racial barriers to segregated education, and this landmark US Supreme Court ruling was implicitly intended to apply to higher education as well. The positive changes for African Americans in removing racial barriers contributed significantly to the civil rights movement and opening avenues of opportunity. Yet, there has always been a fundamental tension between the removal of the vestiges of racial segregation to create equal educational opportunity, and the activist stance of addressing historical and current discriminatory educational policies. This is evident in the recent higher education desegregation and affirmative cases as the Federal Courts advocate the colour‐blind interpretation of higher education desegregation law and educational policy, while African Americans argue in favour of the enhancement of the public Historically Black Colleges and Universities and the explicit use of race as a form of diversity. This article examines the salient positions and racial identity politics surrounding this tension. I also argue that broader issues of racial control and power need to be addressed by educational institutions, the courts and the larger society in the debate about race, social justice and the removal of the vestiges of segregation.