We enjoyed reading JAIC's architectural issue (vol. 42, no. 1) and were pleased that two of the six articles in the issue described testing programs where PROSOCO products were evaluated.

“The Rationale for Microabrasive Cleaning: A Case Study for Historic Granite from the Pennsylvania Capitol” describes testing of Sure Klean Restoration Cleaner and Sure Klean Heavy Duty Restoration Cleaner. Although these products were used in dilutions that we recommend, the dwell periods were not. PROSOCO recommends 3–5 minute dwell periods for both products; for testing on this project, the authors extended dwell times to 10 and 15 minutes.

In describing tests results, authors J. Christopher Frey and Timothy Noble state that higher concentrations and increased dwell times resulted in a rough textured, streaky appearance of granite on the test areas. We were not surprised by these results given the length of the dwell periods. Our product literature cautions users about extending the dwell period beyond the recommended 3–5 minutes.

In note 2, the authors express the opinion that it would be difficult to avoid longer dwell periods for Restoration Cleaner and Heavy Duty Restoration Cleaner during construction. We disagree. In our experience with these products during the past 25 years, limiting the dwell period to 3–5 minutes has not been a problem. Used as recommended in our product literature, Restoration Cleaner and Heavy Duty Restoration Cleaner have been used to clean historic structures throughout the United States without damaging the stonework.

We acknowledge that each project has unique requirements and that use of chemical cleaning is not always the best method. We commend the authors on their testing program on this important project and regret that we were not invited to participate in order to assure that these and other potentially more suitable formulations were evaluated in accordance with our recommended procedures.

Evaluation of PROSOCO products also was reported in “Evaluation of Cleaning Methods for the Exterior Brick at the Brooklyn Historical Society.” In section 3.1, authors Claudia Kavenagh and George Wheeler discuss their decision to test only commercially available products, stating that the large scale of the project and the need for product uniformity were factors. Interestingly, testing on this project included a version of our Sure Klean Restoration Cleaner that the authors modified by the addition of a thickener at the job site.

Though the authors succeeded in modifying one of our standard formulations with good success, PROSOCO cannot encourage alterations that go beyond our recommended water dilutions. Doing so may endanger the safety of conservators or contractors whose understanding of cleaning chemistry is most likely more limited.

For this project, PROSOCO was able to supply a packaged, prediluted, thickened cleaner that suited project requirements. Whenever practical, PROSOCO works with consultants to accommodate special needs such as this.

PROSOCO certainly values the testing that is conducted by architectural conservators, and we welcome the opportunity to work with you on projects such as these. We hope to see more articles by Architecture Specialty Group members in future JAIC issues.

Thank you for the opportunity to respond to the PROSOCO letter that commented on our article on cleaning historic granite from the Pennsylvania Capitol. We feel that our study presents a fair and balanced approach to the testing of several different cleaning methods as well as a realistic assessment of potential issues associated with the restoration work. As conservators, we are interested not only in the physicochemical effects that any treatment might produce but also in realistic, practical considerations that could produce undesirable effects if mistakes are made in application.

We believe that observing the recommended dwell time of 3–5 minutes consistently on all surfaces would, at best, have been extremely difficult on a building of this size. Our concern was based partially on previous experience and partially on consultation with well-respected masonry contractors who have (even with proper supervision and regular evaluation) had difficulty in observing very short dwell times in large-scale cleaning. As a practical matter, applicators often treat large surface areas in order to minimize treatment overlap and to adjust for architectural features. The amount of time required to treat and completely rinse large areas can easily exceed 3–5 minutes. Once the likelihood for dwell times longer than those that are recommended by the manufacturer was identified as an issue, it was deemed appropriate to evaluate the effects of prolonged exposure. The results of longer dwell times are in full accordance with the manufacturer's product data; in this case, extended dwell times produced undesirable effects.

Our article discusses the negative consequences of previous inappropriately applied cleaning treatments. Given the problems caused by previous treatments, it would have been irresponsible not to make an effort to understand what might happen if inadvertent errors were made during construction.

The discourse on this subject is both encouraging and enlightening, particularly with regard to product modifications that are not explicitly recommended in product literature and/or have not been documented with previously published technical studies. Additionally, we believe that this discussion reinforces the notion that proper testing, attention to practical considerations, assessment of material concerns, and proper supervision all play significant roles in whether a treatment can be considered appropriate. AIC and the authors contributing to the Architecture Specialty Group issue have performed a tremendous service in contributing knowledge and discussion on these important subjects.

In her review of Dear Print Fan in JAIC (vol. 42, no.1), Peggy Ellis wrote of my contribution, “One would like to know if the engravings are reversed from the corresponding Nanteuil portraits, evidence supporting Burns's suggestion that some pastel portraits were counterproofed” (p. 133). In fact, my argument there (p. 42) is that the “unfinished pastel [nose right] may have been placed face down on the copper plate [nose left]” to which the drawing's outlines were transferred. Thus the image would have been reversed on the copper plate but would not be reversed in the final engraving [nose right] vis-�-vis the original outline (ultimately finished pastel) composition [nose right].