The real boom for young art in Copenhagen came in the autumn of 1917 when Giersing was presiding as the virtual leader of the foremost artists' association of the day, and as the spokes-man for young artists.
In 1917-18 Giersing wrote a series of contributions to the first two years' issues of the young artists' new periodical "Klingen", and the tone there was considerably more aggressive and uncompromising than in the articles he wrote between 1909 and 1913. He appeared less as the spokesman for new ideas, for they were now established, but as the authority answering those who refused to accept the triumph of the new ideas, and as the master encouraging his disciples to fight and endure.
Giersing had access to the press now, and Klingen did what it could to promote him and his ideas because he was an important painter and adept at formulating himself, and not least because a leading figure, a leader and master, was needed.
Giersing's position was secured in the third issue of Klingen from December 1917, in which his painter colleague Sigurd Swane contributed a warm homage to his friend, and where he himself, among other things, published a furious prose poem "Til Klingen", in which he talks of "Making the picture crack, making the lines explode one against the other, the colours rattle with stubborn power and splendour".
November 1918 saw a series of confrontations between militant workers and police in Copenhagen. At the same time, in reaction to the autumn exhibition that year, artists and various groups of journalists and the upper middle classes were carrying on a verbal battle as to whether the stable view of the world could survive. Giersing naturally took part in this in defence of the young artists who were under severe attack.
It was only to be a further year before normal conditions returned and Giersing pronounced himself unable to glimpse the "artists of true fire and blood" who had the patience to conquer the public in some unspecified distant future. But before that, from late 1917 to early 1919, there was no doubt. Everything indicated total victory for the young and the still younger - with Giersing at their head.
In the eventful autumn of 1917 a further watershed occurred in Giersing's private life, when in November he married Besse Syberg. She had been his pupil and was the daughter of his colleague Fritz Syberg. Giersing went for looks, and Besse was not only unusually charming, but she had the special quality of an inner nature and an outward appearance that were similar to those of his mother. She was an ideal version of Mother, ideally equipped for immortalisation on canvas, with a halo around her pageboy hair when the light struck it, and moreover she had since childhood been accustomed to serving as a model.
For the following four or five years she was Giersing's principal model when he was not painting from photographs or from nature. When in 1922 she started training for the stage and soon became a professional, Giersing's sisters came into their own again for a time, but she continued to be his preferred model, whom he never tired of drawing and painting.
In 1916 and 1917 painting from life had played a secondary role. Giersing had painted some realistic pictures of won1en in which the stylisation, restlessness and movement corresponded to a striking new tension in the figure's relationship to the diagonal, with which it refused to harmonise, but that is not how he approached L3esse. She apparently helped him to rise to a more monumentally conceived picture.
The dehumanisation of Giersing's figures has often been remarked on, but the human being or the human qualities had never completely disappeared. What disappeared was the "natural" difference between the individual, the individual subject, and a surrounding objective reality. Everything is of the same stuff. Man is an object, and so it is only logical that Giersing should often hide Besse's face, for the secret and seduction are very much at work, as is usual in Giersing's portraits.
During the first three months of 1918 Giersing sold seven paintings - without exhibiting - and that was a record. From a business point of view it could not have fallen out better that on the 21st March 1918 he had a retrospective exhibition in the Art Association in Copenhagen. Meanwhile, the press did not approve of the post-1915 pictures. A line that was painted as though from a ruler, and a sharp colour contrast were reckoned to be less sensitive than an undulating line and a richly modulated palette within a limited scale. The former was interpreted as an intentional style, the latter as personal artistic sensitivity.
In 1918 Giersing was completely unaffected by the press criticism, for it "is only the fools among the critics who believe that they can teach artists anything", as he wrote in Klingen. And customers had learnt that negative criticism had to be thought of as a guarantee of quality.
The recession after the military end to the Great War in November 1918 was soon to have serious consequences for artistic life in Copenhagen. In the winter of 1918-19 sales were falling, but the frequency of exhibitions and the general desire for confrontation were undiminished.
In January 1919 Giersing, together with Johannes C. Bjerg, organised an ambitious new exhibition entitled "Sculpture, Painting, Music" for which he himself was to provide paintings, Bjerg sculptures and Carl Nielsen together with others the music to be performed amidst the visual exhibits. The idea of linking music to visual art, was not a new discovery of Giersing's. He had experienced it in Paris, and in 1910 he had arranged a matinée at the Ung Dansk Kunst exhibition. The chamber recitals in "Sculpture, Painting, Music" were, as the title suggested, not only conceived as recitals: the intention with the combination of music and visual art was, if not to create a piece of Gesamtkunst, at least to achieve some total experience.
On the 15th January 1919 Giersing attended the famous series of lectures given by Professor Carl Julius Salomonsen under the title of "infectious mental ailments past and present, with special reference to contemporary directions in art". Professor Salomonsen wanted to demonstrate that large parts of modern art were due to an infectious mental illness, dysmorphism, the symptom of which was "distorted and unnatural, usually also ugly and repulsive representations of the products of nature and art". Giersing wrote two replies to Salomonsen and painted a combative picture that must be seen as a reply in the form of a painting. He called this artistic provocation, which was inspired by Carl Nielsen's music, Aladdin's Ecstasy in the Magic Cave. It was a representation of the modern artist who, borne by a happy fate, revels in the magic cave of art. The geometrical simplification and stylisation of the figure, and the unmistakable inspiration from African masks had, in a lithograph from the same time called The God of War expressed a negative, destructive potential.
The hope for a new great age for art and artists, however, was soon dispelled, and only a year later the situation was totally changed. After the Great War Denmark showed no sign of becoming the magic cave of art or artists for which Giersing and the artists of Klingen had hoped.