I rang the doorbell and waited. Perhaps half a minute elapsed before the door opened, and the woman stared at me sullenly. She was tall and very slim, almost skinny, apart from heavy breasts; her dark, shoulder-length hair was streaked with grey, and, apart from skimpy gauze panties that were practically transparent, a thin silver chain encircling her right ankle, and high heels, she was completely naked.

For a moment, I studied her body, my penis stirring involuntarily: her ribcage was clearly defined, and her lush delicately blue-veined breasts were capped with large, heavily stippled aureoles, from which engorged nipples, the size of the top joint of my little finger, jutted aggressively. Her panties covered only the lower half of her slightly curved belly, and several tendrils of greyish hair emerged from the thin translucent material stretched tightly over her pubic mound.

By contrast, her legs were superb, perfectly shaped, their curves accentuated by the chain and her high heels. She was breathing heavily, and I looked up to see her staring at me unfocussed, almost unseeingly, through heavy-lidded, and, I guessed, sex-drugged eyes.

Without a word, she turned and walked inside the flat, and I closed the front door behind me and followed her into the living room, admiring her thin bare shoulders, her tight backside, her panties unsuccessfully straining to restrain her lean buttocks, but leaving more than half of them exposed, and her shapely legs ... He was sitting in the corner of the sofa, and he lazily waved a hand in my direction as the woman crossed the room towards him and caressed his face.

'You took your time, Mum, ' he grinned, 'I was beginning to lose my erection!'

She bent over him, her large breasts dangling, and he gripped one as she kissed him lingeringly, while she rotated her hand on his groin, and then, giving him a final squeeze, she perched on the arm of the sofa beside him. She crossed her bare legs, one foot swinging idly, her shoe dangling as she undid a couple of buttons of his shirt and slipped her hand in, running it over his bare chest.

He reached up to squeeze her lush breast again, and then he looked at me.

'Help yourself to a drink, ' he said, nodding towards a table by the window holding a section of bottles and glasses.

I poured myself a scotch, and added a little water – when I turned back, she was bending to kiss him feverishly, working her mouth on his, and he was fondling her naked breast, and I sat in an armchair at a slight angle, watching them. After a few minutes, he pushed her away, and she sat up, her breasts heaving.

He grinned at me again. 'Now, what's all this about?'

She grabbed his hand and put it on her bare thigh, and he turned his head towards her and kissed her heavy breast, briefly sucking her nipple.

I took a drink from the glass I was holding. 'Wet collodion photography, ' I said. 'I need to know something about it, for the book I'm writing. It involves a photographer working in the latter half of the nineteenth century... '

'Photographing nudes, I bet!'

It was my turn to grin, and I nodded.

'There are plenty of books about it – I can lend you a couple, if you like.'

She dragged his hand to her breast, and again leaned down to kiss him urgently, and I saw him crush her breast in his hand.

'Yes, I've looked at one or two books, but it's not the same as talking to someone who's actually done it, describing what happens, and what it's like, and you're supposed to be something of an expert... '

She slid down onto the sofa beside him, and slid her leg over his thighs, grinding her groin against him, and she kissed him wetly, open-mouthed as she squirmed in his arms, squashing her bare breasts on his chest, and I saw her saliva trickling down his chin.

I notice her dress lying in a crumpled heap in a corner – there was no sign of a bra, and I guessed she hadn't worn one. I opened my notebook, and removed the cap from my pen.

' OK. Well, he wouldn't have much time once he'd started, so he'd pose her beforehand, doubtless having a good feel in the process; he'd have set up the camera on a tripod – a hand-held exposure would be out of the question – focussing it and checking the composition of the picture, and then putting the lens cap on.'

I noticed his trousers were gaping open, and she inserted her hand inside, fondled him, and he slipped his arm round her and stroked her bare shoulder, and she wriggled against him, lifting her face for him to kiss her. I saw their tongues circle each other for a moment, and then he turned his attention back to me.

'Then, when he was ready, he'd pour the collodion on a glass plate, tilting it so that the collodion flowed diagonally from one corner to the opposite one, and then again diagonally from the other corner to the other – the idea would be to get a completely even coating, and then he'd pour the remaining collodion back into the bottle.'

She knelt up beside him, cupping one breast and lifting it, offering it to his mouth, and he sucked her stiff, rubbery nipple, running his hand up her thigh and fondling her bottom, and she repeated the performance with her other breast, rubbing it against his face. He sucked her nipple for a moment or two, and then he slapped her bottom.

'I could do with a drink, Mum.'

She'd lost her shoe, and squirmed round on the sofa to bend over to grope for it, flattening her ripe breasts against her bare thighs, until she found the shoe and slipped it on. She got to her feet, and he slapped her backside again.

We both watched her cross to the table and pour his drink, her free hand between her legs, fondling herself, before picking up the glass and carrying it to him.

She sat on the sofa beside him, spreading her legs wide, and took his hand, sucking his fingers, and then pushing his hand down inside the front of her panties, and through the filmy material I saw his fingers working between her legs. She made a little mewing sound, and lifted one breast to her mouth, kissing it and sucking her nipple, while he continued to fondle her, and more tufts of grey hair escaped from the legs of her panties ... she crossed her gorgeous bare legs, trapping his hand between her thighs...