MITRA Forum Question Details

Hi,

Let's start by having you read through previous posts about similar subjects and then we can focus on subjects that we have not delved into before. The following is a good one:

https://www.artcons.udel.edu/mitra/forums/question?QID=700

This one has some good info in it as well:

https://www.artcons.udel.edu/mitra/forums/question?QID=526

As does this:

https://www.artcons.udel.edu/mitra/forums/question?QID=286

Feel free to ask about anything not covered in those.

Hi Tom

I would have thought that the Ti02, with its sub-micron particle size, would be a poor choice given its lack of tooth. This is very interesting to read.

Tom Mazzullo knows as much about metalpoint as anyone, and covers the traditional gesso option well.   But I love this topic and can't resist adding several more thoughts – I hope some prove helpful to your project. 

The abrasion in a metalpoint ground is primarily created by…

1. High Pigment Volume Concentrate (PVC).  A ground/paint that has a high solid/pigment content relative to the binder, so that the solids/pigments protrude above the surface of the binder.   This creates an irregular, rough surface (on a microscopic level, generally) or "toothiness" that abrades the metal nib.

2. Hardness.  Solids/pigments within a ground are very hard; i.e. have a Moh's Hardness Scale (MHS) rating higher than the metal nib being abraded.  

Of the two I think hardness is as important as toothiness – but first I want to look at a rough surface. 

HIGH PVC/TOOTHINESS.  Metalpoint has no binder. Metal marks hold on via a mix of particles getting trapped within the "nooks and crannies" of a support/ground, along with electrostatic attraction between particles.

If a ground is too smooth – i.e. there are not enough irregularities in the surface - metal marks may, over time, lose their "grip" (so to speak) and a drawing can appear to "fade".

However if a ground is very rough (akin to sandpaper) it has larger and fewer interstices into which metal deposits can lodge.  A large tooth ground also abrades larger metal particles that are less likely to attach to the surface and each other.  So, at some point, too large-toothed a ground makes for less stable metalpoint marks. 

For the above reason I don't generally recommend very rough pastel grounds (I've tried several) for metalpoint.  I realize you like the Golden Pastel and needn't listen to me…. I just want to clarify what I see as potential shortcomings of a very rough ground.

HARDNESS.  To the extent it can be determined, the hardness of the solids/pigments within a ground is one of the most important considerations in creating an abrasive surface.  Simply put, if ground solids are harder than a metal nib being drawn across that surface, the ground abrades the nib.

You can add extra solids/pigments to most grounds to increase both PVC and hardness.  However, too much added solids can lead to chipping/delamination of ground from support, and/or a brittle, friable ground that crumbles under a metal nib.  So, a conservative starting point is adding 5% of the total volume of ground.  If there are no problems, gradually increase the amount.  Material experts generally recommend no more than 10% added solids to an existing ground.  In practice I've added more with success, depending on the binder.  Experiment and test (see below).

TESTING SOLID/PIGMENT CONTENT IN A GROUND

1.  Flexibility.  Apply one or two layers of the amended ground to a flexible support (i.e. 90# watercolor paper).  Gently bend in various directions and see how it reacts.  If the ground cracks or shatters into pieces = too much pigment. (However, for the actual drawing, always apply multiple layers of a high PVC ground to a rigid support, as you're planning to do via HDF).

2.  Adhesion. Do a cross hatch adhesion test to see if there's enough binder for the ground to properly adhere. 

3.  Diluent Sensitivity. For water-soluble grounds, take a wetted Q-tip and rub the surface to see if ground lifts or dissolves (but don't rub too aggressively or you'll merely remove ground through abrasion). The ground should stay put. If you can't see a white ground on a cotton Q-tip, warp the end with a small piece of wet, blue shop rag. 

EXTENDER SOLIDS/PIGMENTS.   Extenders must be inert.  Particle size is best within the .1 to 2 micron size.  A pigment's color and opacity/transparency are also factors.  Additionally, some extenders give unexpected results, i.e. I've found that pumice brings out more of a metal's color.  There are many options, but here are a few of my favorites for increasing abrasion, followed by the MHS rating.  (FYI, a pure silver nib is 2.5 MHS; sterling silver is about 3 MHS).

Bone Ash  3

Zinc White 4 

Pumice 6 

Pyrite 6.5

Titanium White 6.5

Silica 7

Of course, always wear a dust mask when working with powders or sanding a high PVC ground - especially silica!

TINTING A GROUND. Tint with either powdered pigments, dispersions or compatible paints.   I tint with powders only if they're large micron size, low tinting earth pigments (because they disperse readily).  For all other pigments I use a commercially produced dispersion to tint.

HEIGHTENING WITH WHITE. I've used all of the following, at various times, for white highlights on metalpoint, and all have worked well for me, no sinking in.  They have different pros and cons (solubility, density, fineness of line, etc.):  White Chalk, Colored Pencil, Pastel Stick, Chinese White Watercolor, Gouache, Casein, Egg Tempera, Acrylic Paint.  

COMMERCIAL GROUNDS.  Finally, If you're content with Golden's regular Acrylic Ground, that's great.  But I've had a lot more luck with metalpoint on Golden's Sandable Gesso (excellent), Absorbent Ground (good) and their High Load Acrylic Paints (good). 

Two other synthetic polymer grounds that work really well for metalpoint are Art Boards Gesso (one of my favorites) and Natural Pigments Tempera Ground. Both sand well and are nicely abrasive.

Extender solids/pigments may be added to any of these commercial options to increase abrasion or to tint.

My all-time favorite metalpoint ground is Natural Pigments, Rublev Traditional Silverpoint Ground. It comes in powder form and needs to be hydrated (two hours), then warmed in a double boiler. It can be applied right away but, like traditional gesso, becomes smoother if put in the refrigerator overnight, then rewarmed and applied the next day.   Of course, you can make a traditional ground from similar ingredients yourself, but the above is convenient.

I prefer all of the above over traditional gesso for metalpoint – but every metalpoint artist has their favorites, and time will tell what works best for you.  Good luck with your project!

​Hi Ellen

Additionally, I do have in my possession two silver points. One is pure silver, one is sterling. I don't know which is which. Any quick way to tell?

Tom or Brian may be able to answer this better than I, but here are a couple of possiblities...

- Sterling is an alloy of about 92.5% silver + 7.5% copper.  The copper gives a bit more hardness; sterling silver is approx. 3 Mohs hardness whereas pure silver nib 2.5.  Rub each nib over a ground and see if one feels softer, abrades more readily - that would be the pure silver. 

- Silver and copper tarnish differently.  Copper also colors differently depending on what element it reacts with (oxygen, sulfides, ammonia, etc.), transforming to either a reddish brown, black, yellow green, or verdigris. The ground also affects how a metal tarnishes!  Given how unpredictable tarnishing is, tarnish color is not a great predictor of a metal. However, in my experience, sterling, with it's copper component, tends to have a hint of color when it tarnishes; pure silver tends to tarnish a bit darker than sterling.  So you could do accelerated tarnishing and see if you note either of those differences.  A couple of ways to speed up tarnishing:  1. Add a few drops of egg yolk to a ground; 2. Put the metalpoint marks, along with a jar of chopped garlic or onions, or some apple cider vinegar, into a sealed container (like a pyrex dish with a lid) for a day or two.  K. Schadler Tarnishing.png

Golden makes fantastic products, but frankly I very much prefer their other two gessos that I mentioned to their actual silverpoint ground.  I too don't like a plastic feeling to a metalpoint ground.  But if a synthetic polymer ground has a high enough solid content (i.e. a very high PVC), it won't feel overtly plasticy - it feels fairly close to traditional gesso. I would say this is true of the Golden Sandable Gesso, Art Boards Gesso, and Natural Pigments Tempera Ground.  

Please let us know how it all works out.

Koo

Hi

In terms of differentiating .999 from sterling, I will give a very long response to what is really a very short answer.

It would be difficult to differentiate sterling from .999 silver on the small scale, at least if you do not have access to analytical tools. One could perform x-ray fluorescence spectroscopy (XRF) and see if there is any copper (or other alloys as nickel and other metals are also used to harden silver to make serviceable jewelry). There are even non tarnishing silver allows that contain germanium that have the same 92.5% of silver as sterling.

For less instrument heavy analysis, one could do a weight vs volume to determine whether there is any metal in the point other than silver. .999 silver is 10.497 g/cm3, sterling is 10.36 g/(cm3. This would require a very accurate scale as well as enough of the metal to accurately determine its volume to compare to its density.

Outside of XRF and the above, the best means of testing are wet chemical analysis or assay. These require a small amount of material to be permanently removed from the sample. One would likely have to pay a lab for this. There are more simple, DIY chemical spot test that can check for the presence of copper (not how much, but the presence). Here is a link to a paper discussing this: https://www.canada.ca/en/conservation-institute/services/conservation-preservation-publications/canadian-conservation-institute-notes/test-copper-lead.html

Sooo, unless you wanted to spend a lot of time, energy, on ambiguity, and/or money. It is probably fine to just work with empirical tests like, “this feels softer, and I need to resharpen frequently, or this is quite hard.  Even this will not reveal if a metal has been hardened by tempering or even “cold working” as opposed by being inherently harder due to alloy content. It is best to buy from someone you trust. It is usually better to spend one’s precious time as an artist perfecting one’s craft or creating meaningful art while relying on trusted manufacturers to give them quality products with accurately described ingredients. In lieu of that, rather than spending time testing pre-purchased materials, it is really relatively easy to make one's own stylus from a known silver article (silver bullion or bars, .925 silver jewelry, or .90 pre 1965 US dimes, quarters, ½ and dollars in the US. Different dates are appropriate for other countries. Most on this forum know all of this. I write these responses expecting them to be reviewed by neophytes and in the future and it is preferable to write it once rather than many times 😉.

As always, other moderators may know something about this that I do not. I do, however, doubt that they will greatly disagree with my penultimate paragraph 😉

BTW I love that all of the great information were are generating (on this subject and others) is being archived here on MITRA by the University for future readers. Thanks all.

​Brian's point is a good one - much simpler to buy a new nib, less than a $1 on a wire jewelry site.   Thanks for clarifying things, Brian.