"The Scratch Test" Topic

I had a bad experience last year using GW white undercoat sprayed on metal figures. It just rubbed off! So in my search for a better method, I'm trying Halfords white car primer – just sprayed three test figures today. The long wait was down to the fact that they state on the can to use at room temp of 20 degrees, so I had to wait a few months for the summer to arrive. I refuse to spray in the house.

Anyway, whilst I wait for that to dry, I tested a couple of plastic bases. One was sprayed GW acryllic, the other hand painted Humbrol No1 Grey Primer. After leaving them to settle for a couple of days, I did the scratch test today using a fingernail. On the base with the GW acryllic, the paint just came right off. On the base with the Humbrol enamel primer, it stayed on and refused to be scratched off.

So if this Halfords primer doesn't work, I will be returning to the method I used back in the 90s – good old Humbrol enamels, at least for the primer and basecoats.

As a base primer, I've used black spray enamel from Walmart.

Rustoleum white primer from the hardware store is my go-to.

Mr Jones,

This should pass your scratch test. Acid etch primer – I use Clostermans available on ebay but I believe Halfords sell a brand called U-Pol. Available in white, grey and possibly black.

Wash your castings in warm soapy water and rinse in hot water. (Washing up liquid leaves a thin film on the figures which you have to get off.) Let dry. Don't handle them now as you will only put grease back on them, wear latex gloves. Throughly wipe them over with cellulose thinners or a professional degreaser, with kitchen paper towel. Let dry. Soak for 15 – 20 minutes in white vinegar – this is a further degreasing stage but importantly it very slightly etches the metal. Wash off very throughly in hot water and let air dry.

For priming you need a temperature of no less than 60F up to about 75F and relative humidity of lower than 60%. If it's too hot the paint dries in the air before it hits the model and you don't want that as you get a really 'ragged' surface.

If you follow this to the letter you won't be able to scratch off the primer and even using a sharp implement it'll give you a hard time. Basically you are spray etching primer into a clean but microscopically rough (etched) surface.

If you can't be bothered to go through this elaborate method enamel works much better as I believe it cuts through any grease on the surface of the castings. By grease I mean the natural oils from your skins etc. Ask anybody who paints metal professionally, like those spraying cars and they will tell you how important getting really clean metal is to the strength of the bond of the primer to the metal.

One caveat on acid etching and a vinegar soak – if dealing with older casting from the bad old days of whatever 'lead' could be had for casting, you could be setting the stage for lead rot if not already present.

I have seen it 'bloom' on older castings just from the soap and water bath taking off any original oils on the surface. Any residual acidity on a bad alloy would end up rotting.

I have been trying the ammonia soak method on some older castings showing rot, but have not been doing it long enough to verify its effectiveness.

Thanks Timmo, that's useful info.

Gesso, applied with a brush. After many years, it has never failed me.

I've gone to Dupli-color automotive primer (sandable) Seems to work well.

Greetings from New Jersey !

Getting the winter's additions to my lead pile deflashed – five horses to go – ready to sand bottoms of bases smooth, and wash (use heavy-duty deterg like Spic-n-Span, not dishwashing liquid – stuf that keeps milady's hands soft is not good for paint adhesion,)

I have sprayed 'Rust-Oleum Clean Metal Primer' (UPC 0-20066-77808-8) on my figures before, and been very satisfied. Will use it with this batch

Have tried 'vinegar etching' before – overnight soak in a solution of roughly 1 part white vinegar to 5 parts water. Concluded really not making enough difference to be worth trouble.

Good luck and good gaming!

Thanks for the interesting thoughts on vinegar soaking and acid etch. I've got a batch of older figures to prime. To be safe it sounds as if I should actually be priming these with enamel.

One question – I know white enamel can yellow over time – it's happened to me but is it possible for the yellowing to bleed through an acrylic paint job or would the fact that the enamel is totally covered from UV exposure ensure it can't yellow?

Goragrad, could you describe what the 'bloom' looks like so I know what to look out for.

How about trying the Humbrol Grey Primer, No.1? It's quite light.

Powdery grey patches/spots.

I recently had some old Minifig longbowmen I washed in soapy water and after rinsing and drying them on about 8 of the 17 some small patches of rot showed up.

As per previous discussions in arises from a bad alloy or too high a casting temperature. Carbonic acid (CO2 and water) in the air creates a lead carbonate that just keeps reacting.

You can knock the rot off with hydrochloric, but that leaves the metal still with an acidic contamination that will continue to produce rot – voice of experience. Ammonia soak followed by distilled water bath and then acetone to dry the mini and an immediate priming is supposed to work.

Will see about a picture as I have some figures that haven't been 'cured' yet.

Thank you. I've painted several hundred older Minifigs castings and haven't had an issue yet. Some of those in my collection are 35+ years old. However, I will keep an eye out for the dreaded bloom now I know what to look for.

Basically if I don't see this bloom after washing is it safe to proceed with acid etch primer? My understanding is that the acid is weak and only active during the curing process.

nnascati +1