I took advantage of the relatively warm dry day we had yesterday to spray primer onto one of the 3D prints from the recent print run (I'm only painting one at the moment as I've promised a few people a look at an unpainted print). In a change from previous models, I'm using a coloured primer, specifically red oxide. This change was motivated by two things, 1) my can of grey primer had run out, and 2) the transfers I'm intending to apply to this wagon are for a red oxide livery. It seems a strange livery to choose, as it is essentially rust coloured (red oxide being another name for Iron Oxide or Fe2O3), but hopefully this will mean that I won't have to apply any paint on top of the primer, which means I should retain more of the detail in the final model.
The main problem I actually had was finding red oxide primer. I checked my local model shop (Antics in Sheffield) but they didn't have any -- although they do stock almost every colour imaginable in both acrylic and enamel. I'd almost given up and resigned myself to using the crimson red I used last time, when Rob Waller blogged about painting his Welsh Highland Railway freight wagons in red oxide. His suggestion (I asked in the comments) was to have a look in a car spares shop or a DIY store rather than a model shop. This was good advise as I managed to pick up a can of red oxide primer in the car spares shop in Penistone. Of course I still don't understand why anyone would want to use a rust coloured primer, surely you would want something where any signs of rust would show up differently and not be hidden by the primer?
As with the grey primer I'd used in the past, the red oxide primer went on easily and helps to bring out the details. Most of the bolts are now visible, and some other fine detail that I couldn't see on the unprimed model stands out nicely (the brake handle is actually thinner than the vertical bar it passes through, but that wasn't visible until I'd sprayed the primer on).
For a change I thought I'd show you the underside of the wagon in some detail, as this gives a better view of the brake system as well as the NEM pockets for attaching couplings. It also allows you to see where I've added liquid gravity to make the model heavier so that it won't bounce of the rails when crossing points etc. I specifically added some cross beams to the underframe, not to strengthen the model but to give me a contained space in which I could glue the extra weight. The next step will be to paint the underframe and metal work black to match the description supplied with the transfers.