I found this photo of the Witteveen High Chair (see also my post Design.nl: Two Dutch Musea Acquire Rietveld Baby Chair) on Dutch Design Double which contains an interview with Ingeborg de Roode, industrial design curator at the Stedelijk Museum Amsterdam (City Museum of Modern Art of Amsterdam) at the occasion of 2010 “Dutch Design Double”, two twinned exhibitions in Amsterdam and Utrecht (Centraal Museum), The netherlands each year.
About the Importance of Gerrit Rietveld’s designs in their collection I noted:
Our latest acquisition, a purchase we made in 2008 with the Centraal Museum and the support of different funding bodies: the Witteveen kinderstoel (Witteveen High Chair). The design from 1918 (just before the famous Red and Blue Chair) was a missing link in the Rietveld collection. Previously, we only knew about it from a black-and-white photo because the only existing example had been lost. It had crossed my mind: ‘If we could only find a second example of it…’ It is very clear in this design how Rietveld was, at that time, on some sort of quest. As well as that, I like the small models that Rietveld made of chairs and buildings: all slotting together very simply.
and
Rietveld‘s work forms one of the key elements of our collection. We have many highlights, such as the aforementioned Witteveen High Chair; an early Red and Blue Chair; the prototype of the Zig-Zag Chair; the Birza Chair, which is made from one sheet of fibreboard; the Harrenstein Bedroom; the Aluminium Chair; and the Steltman Chair.
Finally an interesting piece of information about Rietveld’s Aluminum Chairs:
On 22 October, the results of a research into the four known Aluminium chairs by Rietveld will be presented in the Stedelijk Museum. Three chairs belong to public collections, of which one is in the Stedelijk. And the fourth is from a private collection. With the aluminum armchair, Rietveld experimented with material in combination with form (for instance: holes that were meant to provide more sturdiness) and possible methods of production (industrial with the help of fibre board).