When asked how vitreous enamel may be removed from metal we answer:
1/ by repeatedly heating the enamelled piece and plunging it into iced water. This will remove varying amounts of enamel and is a useful first step before:
2/ wet grinding away with a diamond burr as much as possible of the remaining enamel without damaging the underlying metal. That is the full extent of the advice we would offer publicly.
However, a proprietary glass etchant, Etchall dip 'n etch® manufactured in the USA by B & B Products is used successfully by some enamellers to completely remove the remaining enamel without damaging the metal substrate.
Both dip 'n etch® and the Etchall® cream contain ammonium bifluoride in the amount of 20% i.e. 20g/100g of dip 'n etch® and say so (albeit in small print) on the containers.
There is a widespread belief among users of these and similar ammonium bifluoride based products that they are harmless and somehow inherently "safer" than the better known, highly toxic hydrofluoric acid. This is a potentially dangerous misconception. Ammonium bifluoride presents virtually identical dangers to hydrofluoric acid and in fact forms varying concentrations of hydrofluoric acid when dissolved in water.
Following is an excerpt from a report on the website of Australia’s National Industrial Chemicals Notification and Assessment Scheme. NICNAS scientifically assesses industrial chemicals for their health and environmental effects and makes recommendations for safe use.
"Ammonium bifluoride ( NH4HF2 ) is very soluble in water ... a 2.8g/100g solution of NH4HF2 would produce a ... 1.7g/100 g solution of hydrofluoric acid ( HF ) at pH 1, with 85% of the fluorine atoms in the form of HF. At higher concentrations or higher pH a significant amount of the HF2-- ion is present ... acidified fluorides can produce substantial quantities of HF in solution."
Nevertheless, the chemicals are themselves only potentially dangerous. What is dangerous is ignorance about these and other materials in common domestic use e.g. caustic dishwasher detergents. If you use these materials, be aware of the requirements for handling, storage and ventilation, and the treatments necessary should something go wrong.
Like your 2 year old "helping daddy" in the studio & then sucking her fingers clean.
What kinds of products contain Hydrofluoric acid?
California Poison Control System
Some carwash chemical manufacturers and distributors market their ammonium bifluoride wheel cleaners and rinses as `safe' alternatives to hydrofluoric acid. However, those who use ammonium bifluoride regularly say it can, in some cases, actually be more dangerous ...
Professional Carwashing & Detailing magazine.
Emergency Physicians Warn of Toxic Car Cleaning Products
American College of Emergency Physicians
Hydrogen Fluoride
Chemical Safety Information from Intergovernmental Organizations
Newsgroups: rec.crafts.metalworking
Subject: Re: Etching a line in Glass .
Roger Haar wrote:
.. You can buy glass etching paste in small quantities at most craft stores .. my wife owns an arts and crafts store and sells this stuff. You can buy a wax-like sheet and apply it to glass. This leaves an exposed pattern which creates the area to be etched with a proprietary "non-acidic, non-hazardous cream" (the waxy stuff masks the area not to be etched)
The "non-acidic, non-hazardous" cream is an ammonium bifluoride solution which is hardly either "non-acidic or non-hazardous" along with some thickener (probably a starch) to prevent running.
As a retired chemist I know that you can get some nasty fluoride burns from ammonium bifluoride. An aqueous solution will have a pH of ~2 which of course is acidic. I "innocently" requested an MSDS sheet from the vendor and (found) it avoids providing any useful information.
For the non-chemists, an ammonium bifluoride solution is what you would get if you started with a solution of hydrofluoric acid and added enough ammonium hydroxide to neutralize one half of the acid present.
The etchant from a craft store will etch the glass .. but do be careful about leaving the cream in contact with the skin and do wear appropriate eye protection ......
Roger Haar
