The Waving Flag: Painting Tips #1 - Humbrol Matt Cote

Tuesday 13 May 2008

Painting Tips #1 - Humbrol Matt Cote

Humbrol Matt Cote is my varnish of choice. I have used it for ten years or more on 15 mm wargames figures and can testify to the makers claims that it is hard wearing and doesn't yellow.

Having said that there are a few things that you should bear in mind when using it:

You must ensure that the white layer that separates and settles on the bottom is fully mixed back in before use. Matt Cote is opaque because it contains a suspension of silica. It is this that imparts the matt finish. Over time the silica settles as it's insoluble. So if you don't mix it properly before use you don't have enough matting agent and you get a satin, or even a gloss, finish.

Satin or Gloss Finish
Sometimes, even after thorough mixing, a bottle will not provide a matt finish. The reason for this is that there's insufficient silica in the bottle full stop. The way round this is to let the bottle settle and remove some of the clear top layer until tests show that the varnish is drying flat. I keep the removed liquor and use it to dilute batches occasionally.

No Longer Matt
If you have an old bottle that suddenly starts to dry gloss simply dilute the varnish with a little white spirit. The varnish dries matt because the silica migrates to the surface during drying. With old bottles there is less solvent due to loss over time. This causes the silica to gel. Mixing disperses the gel but the silica isn't mobile enough and doesn't migrate to the surface. Adding a small amount of solvent disperses the gel and restores the matting properties of the varnish.

Using Talc (Added Thu 9 Aug 01, 2018)
If none of the above work then try this tip.  Add small amounts of plain unperfumed talc to the varnish along with some 4-6 mm glass beads.  Sadly there's no hard and fast rule for how much talc you have to add.  It's down to trial and error I'm afraid; although in my experience it's hard to add too much.  The beads are vital as the talc will cause the matting agent to settle far quicker than before.  If you leave the varnish undisturbed for any length of time, a layer of matting agent will gather at the bottom of the jar: the beads will help you re-suspend the original matting agent, and the added talc, before use.

Let me know if you have any tips or tricks.


Vexillia said...

Update: Added tip about adding talc.

Unknown said...

My matte cote was completely settled today after being in storage for 3 years.

What I did to restore my matte cote tonight was I heated water in a small pot. I have thermal resistant gloves, so I just held the matte cote bottle in the water (not touching the metal of the pot) for 1.5 minutes.

Then I shook it up it, stirred it up, and waited for it to cool. When I applied it was matte.

Vexillia said...

Be careful! The hot water will cause a build up of flammable solvent fumes in the bottle. I would use my ultrasonic bath to do this.

Hands said...

Do you thin/dilute your mattcote, or apply it straight from the bottle?

Vexillia said...

It's been that long since I used a fresh bottle I don't really know if my stock has been diluted or not.

It's had talc added, been topped up with fresh varnish, and had white spirit added when it has lost too much solvent. Who can tell?

In general I don't dilute it. If anything the reverse: see "Satin or Gloss Finish" above.

Hands said...

I didn't stir it enough. I get good matte coverage on a single coat. However, if I go back over the coat usually once it visually "dries," I am usually left with a satin coat.

Is this because the underlying matt cote is still technically "wet?" Or is my brush picking up all of the deposited silica?

Vexillia said...

The varnish tends to penetrate the paint layer(s). It looks dry when it isn't. I leave newly varnished figures for at least 4 hours before handling them; preferably longer.

Adding a second coat to any paint or varnish is never a good idea. In this case I don't know the mechanism but it's unlikely to pickup any deposited silica.

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