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When preparing a copper etching plate for etching, it must be degreased completely before putting on the etching ground. Otherwise the acid may "bite" through the ground ("foul biting") in spots not desired. Whiting has been used for degreasing and alcohol has also been used successfully. I was wondering whether using hand dishwashing liquid as a preliminary measure (before the alcohol or whiting) to remove oil-based ink and other substances both degreases -- as I think it may do when washing dishes -- but also adds "grease."

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    $\begingroup$ What do you mean by “grease” being added? $\endgroup$
    – Jon Custer
    Feb 17, 2023 at 1:16
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    $\begingroup$ What is "whiting" ? $\endgroup$
    – Poutnik
    Feb 17, 2023 at 8:31
  • $\begingroup$ @Buttonwood Hmm, that is understandable, but the used context is confusing Whiting has been used for degreasing, like pointing to something else. $\endgroup$
    – Poutnik
    Feb 17, 2023 at 10:28
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    $\begingroup$ @Poutnik "Whiting is used by the craftsman as a cleaning agent to help remove the residues from the work after the soldering operation. Whiting is one of the ingredients in polishing compounds, putties, paints, etc. This soft non-abrasive powder is usually applied with a stiff scrub brush. Its use is recommended particularly on copper foil shades to remove the flux and gum, and to give a high shine to the glass and metal." by whittemoredurgin.com/…. CaCO3 (chalk?) by merriam-webster.com/dictionary/whiting $\endgroup$
    – Buttonwood
    Feb 17, 2023 at 11:58

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There is a large set of chemicals which either can act as a moisturizer and/or emollient by chance, or which are intentionally added to the detergent for this function. You find them in cosmetic shampoos, as well as dishwashing liquids advertised as "especially friendly to the skin of your hands". It can be difficult to get rid of them, one reason why labs active in analytical chemistry (e.g., characterization of surfaces)* are careful when using them / their dishwashers finally rinse the glass ware with deionized water.

To extend Poutnik's answer, the typical suspects are (for example) palmitates, stearyl alcohol and stearyl ethers, squalene, decyl esters, polyethylene glycols (PEG). There equally are some telling generic names for them e.g., lamesoft (BASF), or tegosoft (evonik). At small scale, you can remove them with clean distilled water, followed by a rinse with e.g., isopropanol/rubber alcohol.


* Surface tension, wettability of surfaces, shape of drops sitting on surfaces relate to surface energies, a topic in physical chemistry. One approach to characterize them is literally to place a drop on a surface and to check its shape:

Macro photograph of two droplets, with blue construction lines next to the left-hand one showing the contact angles. The caption reads: Figure 2. Representative image of contact angles before (left) and after epicuticular wax removal (right) from collard leaf.

(edit of an image by Chiu et al.)

Especially with the advent of cell phone cameras, this is an affordable experiment for the undergrad labs. As reported by Chiu et al., students take a couple of photos, fed them into the freely available ImageJ program supplemented by the plugin about contact angles (a link to youtube for a brief tutorial), and determine the contact angle (enclosed by the blue straight lines added to the illustration above). Recording multiple drops per sample improves your evidence by statistics, especially if comparing different samples/PCBs.

For process/quality control, one can hence imagine to record this characteristic angle between a surface of a reference sample deemed clean enough, and distilled water. On any subsequent PCB, one would drop again a drop of distilled water to record anew a couple of photos (and by this, contact angles) about different spots as a check before the board enters the next stage of soldering, coating, etc.

Chiu, Y.-C.; Jenks, M. A.; Richards-Babb, M.; Ratcliff, B. B.; Juvik, J. A.; Ku, K.-M. Demonstrating the Effect of Surfactant on Water Retention of Waxy Leaf Surfaces. J. Chem. Educ. 2017, 94, 230–234; doi 10.1021/acs.jchemed.6b00546.

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Total "degreasing" of skin is undesired and would be harmful in long term.

For that reason, skin washing formulas contain auxiliary components, partly lipophilic, intended to adhere on skin and regulate the level of skin "degreasing". And they partly "distract" the surfactant not to do skin fat emulgation so thoroughly.

The overall effect interferes with the goal to have clean surface.

It is better to use formulas advised to use with gloves (like liquid formulas for manual dishwashing).

Or even better - using pure surfactants intended for labs (like sodium laurylsulfate, or some biodegradable alternatives).

Or, organic solvents as mentioned, but then there can be material-solvent compatibility issue.

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  • $\begingroup$ I believe whiting is calcium carbonate. Thanks all for the thorough answers and comments. $\endgroup$
    – Sketcher
    Feb 17, 2023 at 14:06
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    $\begingroup$ @Sketcher Thanks. Interesting. I have originally thought it was some procedure. :-) $\endgroup$
    – Poutnik
    Feb 17, 2023 at 14:12
  • $\begingroup$ Isn't the subject the copper etching plate, not (human) hands? 'hand dishwashing liquid' as a compound noun? Or just dishwashing liquid - "...is primarily used for hand washing of glasses, plates, cutlery, and cooking utensils in a sink or bowl.". $\endgroup$ Feb 17, 2023 at 22:52
  • $\begingroup$ @PeterMortensen You are right :-) I must have read it wrong. But it would not change the answer much, just putting less stress on the additives. $\endgroup$
    – Poutnik
    Feb 18, 2023 at 4:58
  • $\begingroup$ I initially thought of "grease" in layman's tactile terms as a wet, somewhat viscous and slippery, possibly oily liquid. Yes, the copper plate is the subject, although human hands do manipulate it, sometimes with plastic gloves. In any case, I believe now that a household soap product will not effectively degrease the copper. Thanks again for the comments, which helped to clarify, particularly in light of the skin-related additives in the soap. $\endgroup$
    – Sketcher
    Feb 18, 2023 at 22:26

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